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@@ -2983,7 +2983,7 @@
 </ul></div><div id="menu-toggle"><svg xmlns="http://www.w3.org/2000/svg" style="width:100%; height:100%; stroke:currentColor" viewBox="0 0 120 120">
       <title>Menu</title>
       <path stroke-width="10" stroke-linecap="round" d="M30,60 h60  M30,30 m0,5 h60  M30,90 m0,-5 h60"></path>
-    </svg></div><div id="menu-spacer" class="menu-spacer"></div><div id="menu"><div id="menu-search"><input type="text" id="menu-search-box" placeholder="Search..."><div id="menu-search-results" class="inactive"></div></div><div id="menu-pins"><div class="menu-pane-header">Pins<button class="unpin-all">clear</button></div><ul id="menu-pins-list"></ul></div><div class="menu-pane-header">Table of Contents</div><div id="menu-toc"><ol class="toc"><li><span class="item-toggle">+</span><a href="#messageformat-objects" title="MessageFormat Objects"><span class="secnum">1</span> MessageFormat Objects</a><ol class="toc"><li><span class="item-toggle">+</span><a href="#sec-intl-messageformat-constructor" title="The Intl.MessageFormat Constructor"><span class="secnum">1.1</span> The Intl.MessageFormat Constructor</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat" title="Intl.MessageFormat ( source, [ locales [ , options ] ] )"><span class="secnum">1.1.1</span> Intl.MessageFormat ( <var>source</var>, [ <var>locales</var> [ , <var>options</var> ] ] )</a></li><li><span class="item-toggle-none"></span><a href="#sec-initializemessageformat" title="InitializeMessageFormat ( messageFormat, source, locales, options )"><span class="secnum">1.1.2</span> InitializeMessageFormat ( <var>messageFormat</var>, <var>source</var>, <var>locales</var>, <var>options</var> )</a></li></ol></li><li><span class="item-toggle">+</span><a href="#sec-properties-of-intl-messageformat-constructor" title="Properties of the Intl.MessageFormat Constructor"><span class="secnum">1.2</span> Properties of the Intl.MessageFormat Constructor</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat.prototype" title="Intl.MessageFormat.prototype"><span class="secnum">1.2.1</span> Intl.MessageFormat.prototype</a></li><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat-internal-slots" title="Internal slots"><span class="secnum">1.2.2</span> Internal slots</a></li></ol></li><li><span class="item-toggle">+</span><a href="#sec-properties-of-intl-messageformat-prototype-object" title="Properties of the Intl.MessageFormat Prototype Object"><span class="secnum">1.3</span> Properties of the Intl.MessageFormat Prototype Object</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat.prototype.constructor" title="Intl.MessageFormat.prototype.constructor"><span class="secnum">1.3.1</span> Intl.MessageFormat.prototype.constructor</a></li><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat.prototype-tostringtag" title="Intl.MessageFormat.prototype [ @@toStringTag ]"><span class="secnum">1.3.2</span> Intl.MessageFormat.prototype [ @@toStringTag ]</a></li><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat.prototype.format" title="Intl.MessageFormat.prototype.format ( [ values [ , onError ] ] )"><span class="secnum">1.3.3</span> Intl.MessageFormat.prototype.format ( [ <var>values</var> [ , <var>onError</var> ] ] )</a></li><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat.prototype.formatToParts" title="Intl.MessageFormat.prototype.formatToParts ( [ values [ , onError ] ] )"><span class="secnum">1.3.4</span> Intl.MessageFormat.prototype.formatToParts ( [ <var>values</var> [ , <var>onError</var> ] ] )</a></li><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat.prototype.resolvedoptions" title="Intl.MessageFormat.prototype.resolvedOptions ( )"><span class="secnum">1.3.5</span> Intl.MessageFormat.prototype.resolvedOptions ( )</a></li></ol></li><li><span class="item-toggle-none"></span><a href="#sec-properties-of-intl-messageformat-instances" title="Properties of Intl.MessageFormat Instances"><span class="secnum">1.4</span> Properties of Intl.MessageFormat Instances</a></li><li><span class="item-toggle">+</span><a href="#sec-intl-messageformat-abstracts" title="Abstract Operations for MessageFormat Objects"><span class="secnum">1.5</span> Abstract Operations for MessageFormat Objects</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-getmessagedata" title="GetMessageData ( source )"><span class="secnum">1.5.1</span> GetMessageData ( <var>source</var> )</a></li><li><span class="item-toggle-none"></span><a href="#sec-getmessagefunctions" title="GetMessageFunctions ( userFunctions )"><span class="secnum">1.5.2</span> GetMessageFunctions ( <var>userFunctions</var> )</a></li><li><span class="item-toggle-none"></span><a href="#sec-handlemessageformaterror" title="HandleMessageFormatError ( onError, completionRecord )"><span class="secnum">1.5.3</span> HandleMessageFormatError ( <var>onError</var>, <var>completionRecord</var> )</a></li><li><span class="item-toggle-none"></span><a href="#sec-messagefallbackpart" title="MessageFallbackPart ( mv )"><span class="secnum">1.5.4</span> MessageFallbackPart ( <var>mv</var> )</a></li><li><span class="item-toggle-none"></span><a href="#sec-messagefallbackstring" title="MessageFallbackString ( mv )"><span class="secnum">1.5.5</span> MessageFallbackString ( <var>mv</var> )</a></li><li><span class="item-toggle-none"></span><a href="#sec-messagevaluesource" title="MessageValueSource ( mv )"><span class="secnum">1.5.6</span> MessageValueSource ( <var>mv</var> )</a></li><li><span class="item-toggle-none"></span><a href="#sec-resolveexpression" title="ResolveExpression ( mf, values, onError, expression )"><span class="secnum">1.5.7</span> ResolveExpression ( <var>mf</var>, <var>values</var>, <var>onError</var>, <var>expression</var> )</a></li><li><span class="item-toggle-none"></span><a href="#sec-resolvemessage" title="ResolveMessage ( mf, values, onError )"><span class="secnum">1.5.8</span> ResolveMessage ( <var>mf</var>, <var>values</var>, <var>onError</var> )</a></li><li><span class="item-toggle-none"></span><a href="#sec-selectpattern" title="SelectPattern ( mf, values, onError )"><span class="secnum">1.5.9</span> SelectPattern ( <var>mf</var>, <var>values</var>, <var>onError</var> )</a></li><li><span class="item-toggle-none"></span><a href="#sec-selectvariant" title="SelectVariant ( selectors, variants, onError )"><span class="secnum">1.5.10</span> SelectVariant ( <var>selectors</var>, <var>variants</var>, <var>onError</var> )</a></li></ol></li></ol></li><li><span class="item-toggle-none"></span><a href="#sec-copyright-and-software-license" title="Copyright &amp; Software License"><span class="secnum">A</span> Copyright &amp; Software License</a></li></ol></div></div><div id="spec-container"><h1 class="version">Stage 1 Draft / December 16, 2023</h1><h1 class="title">Intl.MessageFormat</h1>
+    </svg></div><div id="menu-spacer" class="menu-spacer"></div><div id="menu"><div id="menu-search"><input type="text" id="menu-search-box" placeholder="Search..."><div id="menu-search-results" class="inactive"></div></div><div id="menu-pins"><div class="menu-pane-header">Pins<button class="unpin-all">clear</button></div><ul id="menu-pins-list"></ul></div><div class="menu-pane-header">Table of Contents</div><div id="menu-toc"><ol class="toc"><li><span class="item-toggle">+</span><a href="#messageformat-objects" title="MessageFormat Objects"><span class="secnum">1</span> MessageFormat Objects</a><ol class="toc"><li><span class="item-toggle">+</span><a href="#sec-intl-messageformat-constructor" title="The Intl.MessageFormat Constructor"><span class="secnum">1.1</span> The Intl.MessageFormat Constructor</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat" title="Intl.MessageFormat ( source, [ locales [ , options ] ] )"><span class="secnum">1.1.1</span> Intl.MessageFormat ( <var>source</var>, [ <var>locales</var> [ , <var>options</var> ] ] )</a></li><li><span class="item-toggle-none"></span><a href="#sec-initializemessageformat" title="InitializeMessageFormat ( messageFormat, source, locales, options )"><span class="secnum">1.1.2</span> InitializeMessageFormat ( <var>messageFormat</var>, <var>source</var>, <var>locales</var>, <var>options</var> )</a></li></ol></li><li><span class="item-toggle">+</span><a href="#sec-properties-of-intl-messageformat-constructor" title="Properties of the Intl.MessageFormat Constructor"><span class="secnum">1.2</span> Properties of the Intl.MessageFormat Constructor</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat.prototype" title="Intl.MessageFormat.prototype"><span class="secnum">1.2.1</span> Intl.MessageFormat.prototype</a></li><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat-internal-slots" title="Internal slots"><span class="secnum">1.2.2</span> Internal slots</a></li></ol></li><li><span class="item-toggle">+</span><a href="#sec-properties-of-intl-messageformat-prototype-object" title="Properties of the Intl.MessageFormat Prototype Object"><span class="secnum">1.3</span> Properties of the Intl.MessageFormat Prototype Object</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat.prototype.constructor" title="Intl.MessageFormat.prototype.constructor"><span class="secnum">1.3.1</span> Intl.MessageFormat.prototype.constructor</a></li><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat.prototype-tostringtag" title="Intl.MessageFormat.prototype [ @@toStringTag ]"><span class="secnum">1.3.2</span> Intl.MessageFormat.prototype [ @@toStringTag ]</a></li><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat.prototype.format" title="Intl.MessageFormat.prototype.format ( [ values [ , onError ] ] )"><span class="secnum">1.3.3</span> Intl.MessageFormat.prototype.format ( [ <var>values</var> [ , <var>onError</var> ] ] )</a></li><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat.prototype.formatToParts" title="Intl.MessageFormat.prototype.formatToParts ( [ values [ , onError ] ] )"><span class="secnum">1.3.4</span> Intl.MessageFormat.prototype.formatToParts ( [ <var>values</var> [ , <var>onError</var> ] ] )</a></li><li><span class="item-toggle-none"></span><a href="#sec-intl.messageformat.prototype.resolvedoptions" title="Intl.MessageFormat.prototype.resolvedOptions ( )"><span class="secnum">1.3.5</span> Intl.MessageFormat.prototype.resolvedOptions ( )</a></li></ol></li><li><span class="item-toggle-none"></span><a href="#sec-properties-of-intl-messageformat-instances" title="Properties of Intl.MessageFormat Instances"><span class="secnum">1.4</span> Properties of Intl.MessageFormat Instances</a></li><li><span class="item-toggle">+</span><a href="#sec-intl-messageformat-abstracts" title="Abstract Operations for MessageFormat Objects"><span class="secnum">1.5</span> Abstract Operations for MessageFormat Objects</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-getmessagedata" title="GetMessageData ( source )"><span class="secnum">1.5.1</span> GetMessageData ( <var>source</var> )</a></li><li><span class="item-toggle">+</span><a href="#sec-getmessagefunctions" title="GetMessageFunctions ( userFunctions )"><span class="secnum">1.5.2</span> GetMessageFunctions ( <var>userFunctions</var> )</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-messageformat-numberfunctions" title="MessageFormat Number Functions"><span class="secnum">1.5.2.1</span> MessageFormat Number Functions</a></li><li><span class="item-toggle-none"></span><a href="#sec-messageformat-stringfunctions" title="MessageFormat String Functions"><span class="secnum">1.5.2.2</span> MessageFormat String Functions</a></li></ol></li><li><span class="item-toggle">+</span><a href="#sec-createmessageformatcontext" title="CreateMessageFormatContext ( mf, values, onError )"><span class="secnum">1.5.3</span> CreateMessageFormatContext ( <var>mf</var>, <var>values</var>, <var>onError</var> )</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-messagecontextrecord" title="MessageFormatContext Records"><span class="secnum">1.5.3.1</span> MessageFormatContext Records</a></li></ol></li><li><span class="item-toggle">+</span><a href="#sec-resolvemessage" title="ResolveMessage ( ctx )"><span class="secnum">1.5.4</span> ResolveMessage ( <var>ctx</var> )</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-selectpattern" title="SelectPattern ( ctx )"><span class="secnum">1.5.4.1</span> SelectPattern ( <var>ctx</var> )</a></li><li><span class="item-toggle-none"></span><a href="#sec-selectvariant" title="SelectVariant ( ctx, selectors, variants )"><span class="secnum">1.5.4.2</span> SelectVariant ( <var>ctx</var>, <var>selectors</var>, <var>variants</var> )</a></li></ol></li><li><span class="item-toggle">+</span><a href="#sec-resolveexpression" title="ResolveExpression ( ctx, expression )"><span class="secnum">1.5.5</span> ResolveExpression ( <var>ctx</var>, <var>expression</var> )</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-resolvefunction" title="ResolveFunction ( ctx, source, resArg, annotation )"><span class="secnum">1.5.5.1</span> ResolveFunction ( <var>ctx</var>, <var>source</var>, <var>resArg</var>, <var>annotation</var> )</a></li><li><span class="item-toggle-none"></span><a href="#sec-resolveunknown" title="ResolveUnknown ( source, value )"><span class="secnum">1.5.5.2</span> ResolveUnknown ( <var>source</var>, <var>value</var> )</a></li></ol></li><li><span class="item-toggle-none"></span><a href="#sec-formatmarkuppart" title="FormatMarkupPart ( ctx, markup )"><span class="secnum">1.5.6</span> FormatMarkupPart ( <var>ctx</var>, <var>markup</var> )</a></li><li><span class="item-toggle">+</span><a href="#sec-getsource" title="GetSource ( ctx, value )"><span class="secnum">1.5.7</span> GetSource ( <var>ctx</var>, <var>value</var> )</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-messagevaluesource" title="MessageValueSource ( mv )"><span class="secnum">1.5.7.1</span> MessageValueSource ( <var>mv</var> )</a></li></ol></li><li><span class="item-toggle-none"></span><a href="#sec-handlemessageformaterror" title="HandleMessageFormatError ( ctx, completionRecord )"><span class="secnum">1.5.8</span> HandleMessageFormatError ( <var>ctx</var>, <var>completionRecord</var> )</a></li><li><span class="item-toggle">+</span><a href="#sec-resolvefallback" title="ResolveFallback ( source )"><span class="secnum">1.5.9</span> ResolveFallback ( <var>source</var> )</a><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-messagefallbackpart" title="MessageFallbackPart ( source )"><span class="secnum">1.5.9.1</span> MessageFallbackPart ( <var>source</var> )</a></li><li><span class="item-toggle-none"></span><a href="#sec-messagefallbackstring" title="MessageFallbackString ( source )"><span class="secnum">1.5.9.2</span> MessageFallbackString ( <var>source</var> )</a></li></ol></li><li><span class="item-toggle-none"></span><a href="#sec-resolvevalue" title="ResolveValue ( ctx, value )"><span class="secnum">1.5.10</span> ResolveValue ( <var>ctx</var>, <var>value</var> )</a></li></ol></li></ol></li><li><span class="item-toggle-none"></span><a href="#sec-copyright-and-software-license" title="Copyright &amp; Software License"><span class="secnum">A</span> Copyright &amp; Software License</a></li></ol></div></div><div id="spec-container"><h1 class="version">Stage 1 Draft / January 12, 2024</h1><h1 class="title">Intl.MessageFormat</h1>
 
 <emu-clause id="messageformat-objects">
   <h1><span class="secnum">1</span> MessageFormat Objects</h1>
@@ -3006,8 +3006,8 @@ <h1><span class="secnum">1.1.1</span> Intl.MessageFormat ( <var>source</var>, [
         <var>source</var>, <var>locales</var>, and <var>options</var>, the following steps are taken:
       </p>
 
-      <emu-alg><ol><li>If NewTarget is <emu-val>undefined</emu-val>, throw a <emu-val>TypeError</emu-val> exception.</li><li>Let <var>messageFormat</var> be ?&nbsp;OrdinaryCreateFromConstructor(NewTarget, <emu-xref href="#sec-properties-of-intl-messageformat-prototype-object" id="_ref_1"><a href="#sec-properties-of-intl-messageformat-prototype-object">%MessageFormat.prototype%</a></emu-xref>,
-           « <var class="field">[[InitializedMessageFormat]]</var>, <var class="field">[[LocaleMatcher]]</var>, <var class="field">[[MessageData]]</var>, <var class="field">[[RequestedLocales]]</var>, <var class="field">[[Runtime]]</var>&nbsp;»).</li><li>Return ?&nbsp;<emu-xref aoid="InitializeMessageFormat" id="_ref_2"><a href="#sec-initializemessageformat">InitializeMessageFormat</a></emu-xref>(<var>messageFormat</var>, <var>source</var>, <var>locales</var>, <var>options</var>).</li></ol></emu-alg>
+      <emu-alg><ol><li>If NewTarget is <emu-val>undefined</emu-val>, throw a <emu-val>TypeError</emu-val> exception.</li><li>Let <var>messageFormat</var> be ?&nbsp;OrdinaryCreateFromConstructor(NewTarget, <emu-xref href="#sec-properties-of-intl-messageformat-prototype-object" id="_ref_4"><a href="#sec-properties-of-intl-messageformat-prototype-object">%MessageFormat.prototype%</a></emu-xref>,
+           « <var class="field">[[InitializedMessageFormat]]</var>, <var class="field">[[LocaleMatcher]]</var>, <var class="field">[[MessageData]]</var>, <var class="field">[[RequestedLocales]]</var>, <var class="field">[[Runtime]]</var>&nbsp;»).</li><li>Return ?&nbsp;<emu-xref aoid="InitializeMessageFormat" id="_ref_5"><a href="#sec-initializemessageformat">InitializeMessageFormat</a></emu-xref>(<var>messageFormat</var>, <var>source</var>, <var>locales</var>, <var>options</var>).</li></ol></emu-alg>
     </emu-clause>
 
     <emu-clause id="sec-initializemessageformat" aoid="InitializeMessageFormat">
@@ -3020,8 +3020,8 @@ <h1><span class="secnum">1.1.2</span> InitializeMessageFormat ( <var>messageForm
         The following steps are taken:
       </p>
 
-      <emu-alg><ol><li>If <var>source</var> is <emu-val>undefined</emu-val>, throw a <emu-val>TypeError</emu-val> exception.</li><li>Let <var>msgData</var> be ?&nbsp;<emu-xref aoid="GetMessageData" id="_ref_3"><a href="#sec-getmessagedata">GetMessageData</a></emu-xref>(<var>source</var>).</li><li>Let <var>requestedLocales</var> be ?&nbsp;CanonicalizeLocaleList(<var>locales</var>).</li><li>Set <var>options</var> to ?&nbsp;GetOptionsObject(<var>options</var>).</li><li>Let <var>matcher</var> be ?&nbsp;GetOption(<var>options</var>, <emu-val>"localeMatcher"</emu-val>, <emu-const>string</emu-const>,
-           « <emu-val>"lookup"</emu-val>, <emu-val>"best fit"</emu-val>&nbsp;», <emu-val>"best fit"</emu-val>).</li><li>Let <var>userFunctions</var> be ?&nbsp;Get(<var>options</var>, <emu-val>"functions"</emu-val>).</li><li>Let <var>functions</var> be ?&nbsp;<emu-xref aoid="GetMessageFunctions" id="_ref_4"><a href="#sec-getmessagefunctions">GetMessageFunctions</a></emu-xref>(<var>userFunctions</var>).</li><li>Set <var>messageFormat</var>.<var class="field">[[MessageData]]</var> to <var>msgData</var>.</li><li>Set <var>messageFormat</var>.<var class="field">[[RequestedLocales]]</var> to <var>requestedLocales</var>.</li><li>Set <var>messageFormat</var>.<var class="field">[[LocaleMatcher]]</var> to <var>matcher</var>.</li><li>Set <var>messageFormat</var>.<var class="field">[[Functions]]</var> to <var>functions</var>.</li><li>Return <var>messageFormat</var>.</li></ol></emu-alg>
+      <emu-alg><ol><li>If <var>source</var> is <emu-val>undefined</emu-val>, throw a <emu-val>TypeError</emu-val> exception.</li><li>Let <var>msgData</var> be ?&nbsp;<emu-xref aoid="GetMessageData" id="_ref_6"><a href="#sec-getmessagedata">GetMessageData</a></emu-xref>(<var>source</var>).</li><li>Let <var>requestedLocales</var> be ?&nbsp;CanonicalizeLocaleList(<var>locales</var>).</li><li>Set <var>options</var> to ?&nbsp;GetOptionsObject(<var>options</var>).</li><li>Let <var>matcher</var> be ?&nbsp;GetOption(<var>options</var>, <emu-val>"localeMatcher"</emu-val>, <emu-const>string</emu-const>,
+           « <emu-val>"lookup"</emu-val>, <emu-val>"best fit"</emu-val>&nbsp;», <emu-val>"best fit"</emu-val>).</li><li>Let <var>userFunctions</var> be ?&nbsp;Get(<var>options</var>, <emu-val>"functions"</emu-val>).</li><li>Let <var>functions</var> be ?&nbsp;<emu-xref aoid="GetMessageFunctions" id="_ref_7"><a href="#sec-getmessagefunctions">GetMessageFunctions</a></emu-xref>(<var>userFunctions</var>).</li><li>Set <var>messageFormat</var>.<var class="field">[[MessageData]]</var> to <var>msgData</var>.</li><li>Set <var>messageFormat</var>.<var class="field">[[RequestedLocales]]</var> to <var>requestedLocales</var>.</li><li>Set <var>messageFormat</var>.<var class="field">[[LocaleMatcher]]</var> to <var>matcher</var>.</li><li>Set <var>messageFormat</var>.<var class="field">[[Functions]]</var> to <var>functions</var>.</li><li>Return <var>messageFormat</var>.</li></ol></emu-alg>
     </emu-clause>
   </emu-clause>
 
@@ -3036,7 +3036,7 @@ <h1><span class="secnum">1.2</span> Properties of the Intl.MessageFormat Constru
       <h1><span class="secnum">1.2.1</span> Intl.MessageFormat.prototype</h1>
 
       <p>
-        The value of <code>Intl.MessageFormat.prototype</code> is <emu-xref href="#sec-properties-of-intl-messageformat-prototype-object" id="_ref_5"><a href="#sec-properties-of-intl-messageformat-prototype-object">%MessageFormat.prototype%</a></emu-xref>.
+        The value of <code>Intl.MessageFormat.prototype</code> is <emu-xref href="#sec-properties-of-intl-messageformat-prototype-object" id="_ref_8"><a href="#sec-properties-of-intl-messageformat-prototype-object">%MessageFormat.prototype%</a></emu-xref>.
       </p>
       <p>
         This property has the attributes
@@ -3069,7 +3069,7 @@ <h1><span class="secnum">1.3</span> Properties of the Intl.MessageFormat Prototy
       <h1><span class="secnum">1.3.1</span> Intl.MessageFormat.prototype.constructor</h1>
 
       <p>
-        The initial value of <code>Intl.MessageFormat.prototype.constructor</code> is <emu-xref href="#sec-intl-messageformat-constructor" id="_ref_6"><a href="#sec-intl-messageformat-constructor">%MessageFormat%</a></emu-xref>.
+        The initial value of <code>Intl.MessageFormat.prototype.constructor</code> is <emu-xref href="#sec-intl-messageformat-constructor" id="_ref_9"><a href="#sec-intl-messageformat-constructor">%MessageFormat%</a></emu-xref>.
       </p>
     </emu-clause>
 
@@ -3093,7 +3093,7 @@ <h1><span class="secnum">1.3.3</span> Intl.MessageFormat.prototype.format ( [ <v
         <var>values</var> and <var>onError</var>, the following steps are taken:
       </p>
 
-      <emu-alg><ol><li>Let <var>mf</var> be the <emu-val>this</emu-val> value.</li><li>Perform ?&nbsp;RequireInternalSlot(<var>mf</var>, <var class="field">[[InitializedMessageFormat]]</var>).</li><li>Let <var>msg</var> be ?&nbsp;<emu-xref aoid="ResolveMessage" id="_ref_7"><a href="#sec-resolvemessage">ResolveMessage</a></emu-xref>(<var>mf</var>, <var>values</var>, <var>onError</var>).</li><li>Let <var>result</var> be an empty String.</li><li>For each element <var>mv</var> of <var>msg</var>, do<ol><li>If <var>mv</var> is a String, then<ol><li>Let <var>stringValue</var> be <var>mv</var>.</li></ol></li><li>Else,<ol><li>Let <var>toString</var> be ?&nbsp;Get(<var>mv</var>, <emu-val>"toString"</emu-val>).</li><li>Let <var>toStringResult</var> be Completion(Call(<var>toString</var>, <var>mv</var>)).</li><li>If <var>toStringResult</var> is a normal completion, then<ol><li>Let <var>stringValue</var> be <var>toStringResult</var>.<var class="field">[[Value]]</var>.</li></ol></li><li>Else,<ol><li>Perform ?&nbsp;<emu-xref aoid="HandleMessageFormatError" id="_ref_8"><a href="#sec-handlemessageformaterror">HandleMessageFormatError</a></emu-xref>(<var>onError</var>, <var>stringResult</var>).</li><li>Let <var>stringValue</var> be <emu-xref aoid="MessageFallbackString" id="_ref_9"><a href="#sec-messagefallbackstring">MessageFallbackString</a></emu-xref>(<var>mv</var>).</li></ol></li></ol></li><li>Set <var>result</var> to the string-concatenation of <var>result</var> and <var>stringValue</var>.</li></ol></li><li>Return <var>result</var>.</li></ol></emu-alg>
+      <emu-alg><ol><li>Let <var>mf</var> be the <emu-val>this</emu-val> value.</li><li>Perform ?&nbsp;RequireInternalSlot(<var>mf</var>, <var class="field">[[InitializedMessageFormat]]</var>).</li><li>Let <var>ctx</var> be ?&nbsp;<emu-xref aoid="CreateMessageFormatContext" id="_ref_10"><a href="#sec-createmessageformatcontext">CreateMessageFormatContext</a></emu-xref>(<var>mf</var>, <var>values</var>, <var>onError</var>).</li><li>Let <var>msg</var> be ?&nbsp;<emu-xref aoid="ResolveMessage" id="_ref_11"><a href="#sec-resolvemessage">ResolveMessage</a></emu-xref>(<var>ctx</var>).</li><li>Let <var>result</var> be an empty String.</li><li>For each element <var>el</var> of <var>msg</var>, do<ol><li>If <var>el</var> is a String, then<ol><li>Let <var>stringValue</var> be <var>el</var>.</li></ol></li><li>Else if <var>el</var> has a <var class="field">[[MessageValue]]</var> internal slot, then<ol><li>Let <var>mv</var> be <var>el</var>.<var class="field">[[MessageValue]]</var>.</li><li>Assert: <var>mv</var> is an Object.</li><li>Let <var>toString</var> be ?&nbsp;Get(<var>mv</var>, <emu-val>"toString"</emu-val>).</li><li>Let <var>toStringResult</var> be Completion(Call(<var>toString</var>, <var>mv</var>)).</li><li>If <var>toStringResult</var> is a normal completion, then<ol><li>Let <var>stringValue</var> be <var>toStringResult</var>.<var class="field">[[Value]]</var>.</li></ol></li><li>Else,<ol><li>Perform ?&nbsp;<emu-xref aoid="HandleMessageFormatError" id="_ref_12"><a href="#sec-handlemessageformaterror">HandleMessageFormatError</a></emu-xref>(<var>ctx</var>, <var>stringResult</var>).</li><li>Let <var>source</var> be <emu-xref aoid="MessageValueSource" id="_ref_13"><a href="#sec-messagevaluesource">MessageValueSource</a></emu-xref>(<var>mv</var>).</li><li>Let <var>stringValue</var> be <emu-xref aoid="MessageFallbackString" id="_ref_14"><a href="#sec-messagefallbackstring">MessageFallbackString</a></emu-xref>(<var>source</var>).</li></ol></li></ol></li><li>Set <var>result</var> to the string-concatenation of <var>result</var> and <var>stringValue</var>.</li></ol></li><li>Return <var>result</var>.</li></ol></emu-alg>
     </emu-clause>
 
     <emu-clause id="sec-intl.messageformat.prototype.formatToParts">
@@ -3104,7 +3104,7 @@ <h1><span class="secnum">1.3.4</span> Intl.MessageFormat.prototype.formatToParts
         <var>values</var> and <var>onError</var>, the following steps are taken:
       </p>
 
-      <emu-alg><ol><li>Let <var>mf</var> be the <emu-val>this</emu-val> value.</li><li>Perform ?&nbsp;RequireInternalSlot(<var>mf</var>, <var class="field">[[InitializedMessageFormat]]</var>).</li><li>Let <var>msg</var> be ?&nbsp;<emu-xref aoid="ResolveMessage" id="_ref_10"><a href="#sec-resolvemessage">ResolveMessage</a></emu-xref>(<var>mf</var>, <var>values</var>, <var>onError</var>).</li><li>Let <var>result</var> be an empty List of Objects.</li><li>For each element <var>mv</var> of <var>msg</var>, do<ol><li>If <var>mv</var> is a String, then<ol><li>Let <var>textPart</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>textPart</var>, <emu-val>"type"</emu-val>, <emu-val>"text"</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>textPart</var>, <emu-val>"value"</emu-val>, <var>mv</var>).</li><li>Append <var>textPart</var> to <var>result</var>.</li></ol></li><li>Else,<ol><li>Let <var>toParts</var> be ?&nbsp;Get(<var>mv</var>, <emu-val>"toParts"</emu-val>).</li><li>Let <var>partResult</var> be Completion(Call(<var>toParts</var>, <var>mv</var>)).</li><li>If <var>partResult</var> is a normal completion, then<ol><li>Let <var>parts</var> be <var>partResult</var>.<var class="field">[[Value]]</var>.</li><li>For each <var>part</var> of <var>parts</var>, append <var>part</var> to <var>result</var>.</li></ol></li><li>Else,<ol><li>Perform ?&nbsp;<emu-xref aoid="HandleMessageFormatError" id="_ref_11"><a href="#sec-handlemessageformaterror">HandleMessageFormatError</a></emu-xref>(<var>onError</var>, <var>partResult</var>).</li><li>Let <var>fallbackPart</var> be <emu-xref aoid="MessageFallbackPart" id="_ref_12"><a href="#sec-messagefallbackpart">MessageFallbackPart</a></emu-xref>(<var>mv</var>).</li><li>Append <var>fallbackPart</var> to <var>result</var>.</li></ol></li></ol></li></ol></li><li>Return CreateArrayFromList(<var>result</var>).</li></ol></emu-alg>
+      <emu-alg><ol><li>Let <var>mf</var> be the <emu-val>this</emu-val> value.</li><li>Perform ?&nbsp;RequireInternalSlot(<var>mf</var>, <var class="field">[[InitializedMessageFormat]]</var>).</li><li>Let <var>ctx</var> be ?&nbsp;<emu-xref aoid="CreateMessageFormatContext" id="_ref_15"><a href="#sec-createmessageformatcontext">CreateMessageFormatContext</a></emu-xref>(<var>mf</var>, <var>values</var>, <var>onError</var>).</li><li>Let <var>msg</var> be ?&nbsp;<emu-xref aoid="ResolveMessage" id="_ref_16"><a href="#sec-resolvemessage">ResolveMessage</a></emu-xref>(<var>ctx</var>).</li><li>Let <var>result</var> be an empty List of Objects.</li><li>For each element <var>mv</var> of <var>msg</var>, do<ol><li>If <var>el</var> is a String, then<ol><li>Let <var>textPart</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>textPart</var>, <emu-val>"type"</emu-val>, <emu-val>"text"</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>textPart</var>, <emu-val>"value"</emu-val>, <var>el</var>).</li><li>Append <var>textPart</var> to <var>result</var>.</li></ol></li><li>Else if <var>el</var> has a <var class="field">[[MessageMarkup]]</var> internal slot, then<ol><li>Let <var>markup</var> be ?&nbsp;<emu-xref aoid="FormatMarkupPart" id="_ref_17"><a href="#sec-formatmarkuppart">FormatMarkupPart</a></emu-xref>(<var>ctx</var>, <var>el</var>.<var class="field">[[MessageMarkup]]</var>).</li><li>Append <var>markup</var> to <var>result</var></li></ol></li><li>Else,<ol><li>Let <var>mv</var> be <var>el</var>.<var class="field">[[MessageValue]]</var>.</li><li>Assert: <var>mv</var> is an Object.</li><li>Let <var>toParts</var> be ?&nbsp;Get(<var>mv</var>, <emu-val>"toParts"</emu-val>).</li><li>Let <var>partResult</var> be Completion(Call(<var>toParts</var>, <var>mv</var>)).</li><li>If <var>partResult</var> is a normal completion, then<ol><li>Let <var>parts</var> be <var>partResult</var>.<var class="field">[[Value]]</var>.</li><li>For each element <var>part</var> of <var>parts</var>, append <var>part</var> to <var>result</var>.</li></ol></li><li>Else,<ol><li>Perform ?&nbsp;<emu-xref aoid="HandleMessageFormatError" id="_ref_18"><a href="#sec-handlemessageformaterror">HandleMessageFormatError</a></emu-xref>(<var>ctx</var>, <var>partResult</var>).</li><li>Let <var>source</var> be <emu-xref aoid="MessageValueSource" id="_ref_19"><a href="#sec-messagevaluesource">MessageValueSource</a></emu-xref>(<var>mv</var>).</li><li>Let <var>fallbackPart</var> be <emu-xref aoid="MessageFallbackPart" id="_ref_20"><a href="#sec-messagefallbackpart">MessageFallbackPart</a></emu-xref>(<var>source</var>).</li><li>Append <var>fallbackPart</var> to <var>result</var>.</li></ol></li></ol></li></ol></li><li>Return CreateArrayFromList(<var>result</var>).</li></ol></emu-alg>
     </emu-clause>
 
     <emu-clause id="sec-intl.messageformat.prototype.resolvedoptions">
@@ -3153,7 +3153,7 @@ <h1><span class="secnum">1.3.5</span> Intl.MessageFormat.prototype.resolvedOptio
     <h1><span class="secnum">1.4</span> Properties of Intl.MessageFormat Instances</h1>
 
     <p>
-      Intl.MessageFormat instances are ordinary objects that inherit properties from <emu-xref href="#sec-properties-of-intl-messageformat-prototype-object" id="_ref_13"><a href="#sec-properties-of-intl-messageformat-prototype-object">%MessageFormat.prototype%</a></emu-xref>.
+      Intl.MessageFormat instances are ordinary objects that inherit properties from <emu-xref href="#sec-properties-of-intl-messageformat-prototype-object" id="_ref_21"><a href="#sec-properties-of-intl-messageformat-prototype-object">%MessageFormat.prototype%</a></emu-xref>.
     </p>
 
     <p>
@@ -3169,13 +3169,17 @@ <h1><span class="secnum">1.4</span> Properties of Intl.MessageFormat Instances</
         <var class="field">[[LocaleMatcher]]</var> is one of the String values <emu-val>"lookup"</emu-val> or <emu-val>"best fit"</emu-val>,
         identifying the locale matcher used.
       </li>
-      <li><var class="field">[[MessageData]]</var> is an Object ...TODO</li>
+      <li>
+        <var class="field">[[MessageData]]</var> is an Object conforming to the
+        <a href="https://github.com/unicode-org/message-format-wg/blob/main/spec/data-model/message.json">JSON Schema definition</a>
+        of the Unicode MessageFormat 2.0 specification.
+      </li>
       <li>
         <var class="field">[[RequestedLocales]]</var> is a List of String values
         with the canonicalized language tags of the requested locales
         to use for message formatting.
       </li>
-      <li><var class="field">[[Functions]]</var> is an Object ...TODO</li>
+      <li><var class="field">[[Functions]]</var> is an Object with function object values.</li>
     </ul>
   </emu-clause>
 
@@ -3199,95 +3203,225 @@ <h1><span class="secnum">1.5.1</span> GetMessageData ( <var>source</var> )</h1>
 
     <emu-clause id="sec-getmessagefunctions" type="abstract operation" aoid="GetMessageFunctions">
       <h1><span class="secnum">1.5.2</span> GetMessageFunctions ( <var>userFunctions</var> )</h1>
-      <p>The abstract operation GetMessageFunctions takes argument <var>userFunctions</var> (an Object or undefined) and returns a Record. It determines the functions available during message formatting. It performs the following steps when called:</p>
-
-      <emu-alg><ol><li>...TODO</li></ol></emu-alg>
+      <p>The abstract operation GetMessageFunctions takes argument <var>userFunctions</var> (an Object or undefined) and returns an Object. It determines the functions available during message formatting. It performs the following steps when called:</p>
+
+      <emu-alg><ol><li>Let <var>numberSteps</var> be the algorithm steps defined in <emu-xref href="#sec-messageformat-numberfunctions" id="_ref_1"><a href="#sec-messageformat-numberfunctions">1.5.2.1</a></emu-xref>.</li><li>Let <var>number</var> be CreateBuiltinFunction(<var>numberSteps</var>, <emu-val>3</emu-val>, <emu-val>"number"</emu-val>, «&nbsp;»).</li><li>Let <var>stringSteps</var> be the algorithm steps defined in <emu-xref href="#sec-messageformat-stringfunctions" id="_ref_2"><a href="#sec-messageformat-stringfunctions">1.5.2.2</a></emu-xref>.</li><li>Let <var>string</var> be CreateBuiltinFunction(<var>stringSteps</var>, <emu-val>3</emu-val>, <emu-val>"string"</emu-val>, «&nbsp;»).</li><li>Let <var>functions</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>functions</var>, <emu-val>"number"</emu-val>, <var>number</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>functions</var>, <emu-val>"string"</emu-val>, <var>string</var>).</li><li>For each String <var>name</var> of ?&nbsp;EnumerableOwnProperties(<var>userFunctions</var>, <emu-const>key</emu-const>),<ol><li>Let <var>func</var> be ?&nbsp;Get(<var>userFunctions</var>, <var>name</var>).</li><li>If IsCallable(<var>func</var>) is <emu-val>true</emu-val>, then<ol><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>functions</var>, <var>name</var>, <var>func</var>).</li></ol></li><li>Else,<ol><li>Throw a <emu-val>TypeError</emu-val> exception.</li></ol></li></ol></li><li>Return <var>functions</var>.</li></ol></emu-alg>
+
+      <emu-clause id="sec-messageformat-numberfunctions">
+        <h1><span class="secnum">1.5.2.1</span> MessageFormat Number Functions</h1>
+        <p>
+          A MessageFormat number function is an anonymous built-in function.
+        </p>
+        <p>
+          When a MessageFormat number function is called with arguments <var>funcCtx</var> (an Object), <var>options</var> (an Object), and <var>input</var> (an ECMAScript language value), the following steps are taken:
+        </p>
+
+        <emu-alg><ol><li>Let <var>locale</var> be !&nbsp;Get(<var>funcCtx</var>, <emu-val>"locale"</emu-val>).</li><li>Let <var>localeMatcher</var> be !&nbsp;Get(<var>funcCtx</var>, <emu-val>"localeMatcher"</emu-val>).</li><li>Let <var>source</var> be !&nbsp;Get(<var>funcCtx</var>, <emu-val>"source"</emu-val>).</li><li>Let <var>opts</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>opt</var>, <emu-val>"localeMatcher"</emu-val>, <var>localeMatcher</var>).</li><li>If <var>input</var> is a String, then<ol><li>Set <var>input</var> to ?&nbsp;Call(JSON.parse, %JSON%, « <var>input</var>&nbsp;»).</li></ol></li><li>Else if <var>input</var> is an Object, then<ol><li>Let <var>valueOf</var> be ?&nbsp;Get(<var>input</var>, <emu-val>"valueOf"</emu-val>).</li><li>If IsCallable(<var>valueOf</var>) is <emu-val>true</emu-val>, then<ol><li>Let <var>inputOptions</var> be ?&nbsp;Get(<var>input</var>, <emu-val>"options"</emu-val>).</li><li>Perform ?&nbsp;Call(Object.assign, <emu-val>undefined</emu-val>, « <var>opts</var>, <var>inputOptions</var>&nbsp;»).</li><li>Set <var>input</var> to ?&nbsp;Call(<var>valueOf</var>, <var>input</var>).</li></ol></li></ol></li><li>If <var>input</var> is not a Number and <var>input</var> is not a BigInt, throw a <emu-val>TypeError</emu-val> exception.</li><li>Let <var>numberOptions</var> be « <emu-val>"minimumIntegerDigits"</emu-val>, <emu-val>"minimumFractionDigits"</emu-val>, <emu-val>"maximumFractionDigits"</emu-val>, <emu-val>"minimumSignificantDigits"</emu-val>, <emu-val>"maximumSignificantDigits"</emu-val>, <emu-val>"roundingIncrement"</emu-val>&nbsp;».</li><li>Let <var>booleanOptions</var> be « <emu-val>"useGrouping"</emu-val>&nbsp;».</li><li>Let <var>select</var> be <emu-val>"cardinal"</emu-val>.</li><li>For each String <var>optName</var> of ?&nbsp;EnumerableOwnProperties(<var>options</var>, <emu-const>key</emu-const>),<ol><li>If <var>optName</var> is not <emu-val>"localeMatcher"</emu-val> and <var>optName</var> is not <emu-val>"type"</emu-val>, then<ol><li>If <var>optValue</var> is an Object, then<ol><li>Let <var>optValueOf</var> be ?&nbsp;Get(<var>optValue</var>, <emu-val>"valueOf"</emu-val>).</li><li>If IsCallable(<var>optValueOf</var>) is <emu-val>true</emu-val>, then<ol><li>Set <var>optValue</var>_ to ?&nbsp;Call(<var>optValueOf</var>, <var>optValue</var>).</li></ol></li></ol></li><li>If <var>optName</var> is <emu-val>"select"</emu-val>, then<ol><li>If <var>optValue</var> is <emu-val>"ordinal"</emu-val> or <var>optValue</var> is <emu-val>"exact"</emu-val>, then<ol><li>Set <var>select</var> to <var>optValue</var></li></ol></li><li>Else if <var>optValue</var> is not <emu-val>"plural"</emu-val>, then<ol><li>Throw a <emu-val>RangeError</emu-val> exception.</li></ol></li></ol></li><li>Else,<ol><li>If <var>optValue</var> is a String, then<ol><li>If <var>numberOptions</var> contains <var>optName</var>, then<ol><li>Set <var>optValue</var> to ToNumber(<var>optValue</var>).</li></ol></li><li>Else if <var>booleanOptions</var> contains <var>optName</var>, then<ol><li>If <var>optValue</var> is <emu-val>"true"</emu-val>, then<ol><li>Set <var>optValue</var> to <emu-val>true</emu-val>.</li></ol></li><li>Else if <var>optValue</var> is <emu-val>"false"</emu-val>, then<ol><li>Set <var>optValue</var> to <emu-val>false</emu-val>.</li></ol></li></ol></li></ol></li><li>Perform ?&nbsp;Set(<var>opts</var>, <var>optName</var>, <var>optValue</var>, <emu-val>true</emu-val>).</li></ol></li></ol></li></ol></li><li>Let <var>numberFormat</var> be ?&nbsp;Construct(%Intl.NumberFormat%, « <var>locale</var>, <var>opts</var>&nbsp;»).</li><li>If <var>select</var> is <emu-val>"exact"</emu-val>, then<ol><li>Perform ?&nbsp;<var>opts</var>.<var class="field">[[Delete]]</var>(<emu-val>"type"</emu-val>).</li><li>Let <var>pluralRules</var> be <emu-val>undefined</emu-val>.</li></ol></li><li>Else,<ol><li>Perform ?&nbsp;Set(<var>opts</var>, <emu-val>"type"</emu-val>, <var>select</var>, <emu-val>true</emu-val>).</li><li>Let <var>pluralRules</var> be ?&nbsp;Construct(%Intl.PluralRules%, « <var>locale</var>, <var>opts</var>&nbsp;»).</li></ol></li><li>Let <var>selectKeyClosure</var> be a new Abstract Closure with parameters (<var>keys</var>) that captures <var>input</var> and <var>pluralRules</var> and performs the following steps when called:<ol><li>Let <var>keyList</var> be ?&nbsp;CreateListFromArrayLike(<var>keys</var>, « String&nbsp;»).</li><li>Let <var>str</var> be ?&nbsp;ToString(<var>input</var>).</li><li>If <var>keyList</var> contains <var>str</var>, return <var>str</var>.</li><li>If <var>pluralRules</var> is not <emu-val>undefined</emu-val>, then<ol><li>Let <var>category</var> be ?&nbsp;Call(Intl.PluralRules.prototype.select, <var>pluralRules</var>, « <var>input</var>&nbsp;»).</li><li>If <var>keyList</var> contains <var>category</var>, return <var>category</var>.</li></ol></li><li>Return <emu-val>null</emu-val>.</li></ol></li><li>Let <var>selectKey</var> be CreateBuiltinFunction(<var>selectKeyClosure</var>, <emu-val>1</emu-val>, <emu-val>"selectKey"</emu-val>, «&nbsp;»).</li><li>Let <var>toPartsClosure</var> be a new Abstract Closure with no parameters that captures <var>input</var>, <var>source</var>, and <var>numberFormat</var> and performs the following steps when called:<ol><li>Let <var>parts</var> be ?&nbsp;Call(Intl.NumberFormat.prototype.formatToParts, <var>nf</var>, « <var>input</var>&nbsp;»).</li><li>Let <var>result</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>result</var>, <emu-val>"type"</emu-val>, <emu-val>"number"</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>result</var>, <emu-val>"source"</emu-val>, <var>source</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>result</var>, <emu-val>"locale"</emu-val>, <var>numberFormat</var>.<var class="field">[[Locale]]</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>result</var>, <emu-val>"parts"</emu-val>, <var>parts</var>).</li><li>Return CreateArrayFromList(« <var>result</var>&nbsp;»).</li></ol></li><li>Let <var>toParts</var> be CreateBuiltinFunction(<var>toPartsClosure</var>, <emu-val>0</emu-val>, <emu-val>"toParts"</emu-val>, «&nbsp;»).</li><li>Let <var>toStringClosure</var> be a new Abstract Closure with no parameters that captures <var>input</var> and <var>numberFormat</var> and performs the following steps when called:<ol><li>Return ?&nbsp;Call(Intl.NumberFormat.prototype.format, <var>nf</var>, « <var>input</var>&nbsp;»).</li></ol></li><li>Let <var>toString</var> be CreateBuiltinFunction(<var>toStringClosure</var>, <emu-val>0</emu-val>, <emu-val>"toString"</emu-val>, «&nbsp;»).</li><li>Let <var>valueOfClosure</var> be a new Abstract Closure with no parameters that captures <var>input</var> and performs the following steps when called:<ol><li>Return <var>input</var>.</li></ol></li><li>Let <var>valueOf</var> be CreateBuiltinFunction(<var>valueOfClosure</var>, <emu-val>0</emu-val>, <emu-val>"valueOf"</emu-val>, «&nbsp;»).</li><li>Let <var>mv</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"type"</emu-val>, <emu-val>"number"</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"source"</emu-val>, <var>source</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"locale"</emu-val>, <var>numberFormat</var>.<var class="field">[[Locale]]</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"options"</emu-val>, <var>opts</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"selectKey"</emu-val>, <var>selectKey</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"toParts"</emu-val>, <var>toParts</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"toString"</emu-val>, <var>toString</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"valueOf"</emu-val>, <var>valueOf</var>).</li><li>Return <var>mv</var>.</li></ol></emu-alg>
+
+        <p>
+          The <emu-val>"length"</emu-val> property of a MessageFormat number function is <emu-val>3</emu-val>.
+        </p>
+      </emu-clause>
+
+      <emu-clause id="sec-messageformat-stringfunctions">
+        <h1><span class="secnum">1.5.2.2</span> MessageFormat String Functions</h1>
+        <p>
+          A MessageFormat string function is an anonymous built-in function.
+        </p>
+        <p>
+          When a MessageFormat string function is called with arguments <var>funcCtx</var> (an Object), <var>options</var> (an Object), and <var>input</var> (an ECMAScript language value), the following steps are taken:
+        </p>
+
+        <emu-alg><ol><li>Let <var>str</var> be ?&nbsp;ToString(<var>input</var>).</li><li>Let <var>selectKeyClosure</var> be a new Abstract Closure with parameters (<var>keys</var>) that captures <var>str</var> and performs the following steps when called:<ol><li>Let <var>keyList</var> be ?&nbsp;CreateListFromArrayLike(<var>keys</var>, « String&nbsp;»).</li><li>If <var>keyList</var> contains <var>str</var>, return <var>str</var>.</li><li>Else, return <emu-val>null</emu-val>.</li></ol></li><li>Let <var>selectKey</var> be CreateBuiltinFunction(<var>selectKeyClosure</var>, <emu-val>1</emu-val>, <emu-val>"selectKey"</emu-val>, «&nbsp;»).</li><li>Let <var>toPartsClosure</var> be a new Abstract Closure with no parameters that captures <var>funcCtx</var> and <var>str</var> and performs the following steps when called:<ol><li>Let <var>source</var> be !&nbsp;Get(<var>funcCtx</var>, <emu-val>"source"</emu-val>).</li><li>Let <var>locale</var> be !&nbsp;Get(<var>funcCtx</var>, <emu-val>"locale"</emu-val>).</li><li>Let <var>locale0</var> be !&nbsp;Get(<var>locale</var>, <emu-val>"0"</emu-val>).</li><li>Let <var>result</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>result</var>, <emu-val>"type"</emu-val>, <emu-val>"string"</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>result</var>, <emu-val>"source"</emu-val>, <var>source</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>result</var>, <emu-val>"locale"</emu-val>, <var>locale0</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>result</var>, <emu-val>"value"</emu-val>, <var>str</var>).</li><li>Return CreateArrayFromList(« <var>result</var>&nbsp;»).</li></ol></li><li>Let <var>toParts</var> be CreateBuiltinFunction(<var>toPartsClosure</var>, <emu-val>0</emu-val>, <emu-val>"toParts"</emu-val>, «&nbsp;»).</li><li>Let <var>toStringClosure</var> be a new Abstract Closure with no parameters that captures <var>str</var> and performs the following steps when called:<ol><li>Return <var>str</var>.</li></ol></li><li>Let <var>toString</var> be CreateBuiltinFunction(<var>toStringClosure</var>, <emu-val>0</emu-val>, <emu-val>"toString"</emu-val>, «&nbsp;»).</li><li>Let <var>valueOf</var> be CreateBuiltinFunction(<var>toStringClosure</var>, <emu-val>0</emu-val>, <emu-val>"valueOf"</emu-val>, «&nbsp;»).</li><li>Let <var>mv</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"type"</emu-val>, <emu-val>"number"</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"source"</emu-val>, <var>source</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"locale"</emu-val>, <var>numberFormat</var>.<var class="field">[[Locale]]</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"options"</emu-val>, <var>opts</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"selectKey"</emu-val>, <var>selectKey</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"toParts"</emu-val>, <var>toParts</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"toString"</emu-val>, <var>toString</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"valueOf"</emu-val>, <var>valueOf</var>).</li><li>Return <var>mv</var>.</li></ol></emu-alg>
+
+        <p>
+          The <emu-val>"length"</emu-val> property of a MessageFormat string function is <emu-val>3</emu-val>.
+        </p>
+      </emu-clause>
     </emu-clause>
 
-    <emu-clause id="sec-handlemessageformaterror" type="abstract operation" aoid="HandleMessageFormatError">
-      <h1><span class="secnum">1.5.3</span> HandleMessageFormatError ( <var>onError</var>, <var>completionRecord</var> )</h1>
-      <p>The abstract operation HandleMessageFormatError takes arguments <var>onError</var> (a Function or undefined) and <var>completionRecord</var> (a Completion Record). It handles errors during formatting. It performs the following steps when called:</p>
+    <emu-clause id="sec-createmessageformatcontext" type="abstract operation" aoid="CreateMessageFormatContext">
+      <h1><span class="secnum">1.5.3</span> CreateMessageFormatContext ( <var>mf</var>, <var>values</var>, <var>onError</var> )</h1>
+      <p>The abstract operation CreateMessageFormatContext takes arguments <var>mf</var> (an Object), <var>values</var> (an Object or undefined), and <var>onError</var> (a Function or undefined) and returns a <emu-xref href="#messageformatcontext-record" id="_ref_22"><a href="#messageformatcontext-record">MessageFormatContext Record</a></emu-xref>. It initializes the <emu-xref href="#messageformatcontext-record" id="_ref_23"><a href="#messageformatcontext-record">MessageFormatContext Record</a></emu-xref> used for pattern selection and formatting. It performs the following steps when called:</p>
+
+      <emu-alg><ol><li>Let <var>localVars</var> be OrdinaryObjectCreate(<emu-val>null</emu-val>).</li><li>Let <var>msgData</var> be <var>mf</var>.<var class="field">[[MessageData]]</var>.</li><li>Let <var>declArray</var> be ?&nbsp;Get(<var>msgData</var>, <emu-val>"declarations"</emu-val>).</li><li>Let <var>declList</var> be ?&nbsp;CreateListFromArrayLike(<var>declArray</var>).</li><li>For each element <var>decl</var> of <var>declList</var>,<ol><li>Let <var>declName</var> be ?&nbsp;Get(<var>decl</var>, <emu-val>"name"</emu-val>).</li><li>Let <var>declValue</var> be OrdinaryObjectCreate(<emu-val>null</emu-val>, « <var class="field">[[UnresolvedDeclaration]]</var>&nbsp;»).</li><li>Set <var>declValue</var>.<var class="field">[[UnresolvedDeclaration]]</var> to <var>decl</var>.</li><li>Perform ?&nbsp;Set(<var>localVars</var>, <var>declName</var>, <var>declValue</var>, <emu-val>true</emu-val>).</li></ol></li><li>Let <var>ctx</var> be a new Record.</li><li>Set <var>ctx</var>.<var class="field">[[LocalVariables]]</var> to <var>localVars</var>.</li><li>Set <var>ctx</var>.<var class="field">[[MessageFormat]]</var> to <var>mf</var>.</li><li>Set <var>ctx</var>.<var class="field">[[OnError]]</var> to <var>onError</var>.</li><li>Set <var>ctx</var>.<var class="field">[[Values]]</var> to ?&nbsp;GetOptionsObject(<var>values</var>).</li><li>Return <var>ctx</var>.</li></ol></emu-alg>
+
+      <emu-clause id="sec-messagecontextrecord">
+        <h1><span class="secnum">1.5.3.1</span> MessageFormatContext Records</h1>
+        <p>
+          A <dfn id="messageformatcontext-record" tabindex="-1">MessageFormatContext Record</dfn> is used to hold the data required during the formatting of a message.
+          It has the fields defined in <emu-xref href="#table-messageformatcontext-record" id="_ref_3"><a href="#table-messageformatcontext-record">Table 2</a></emu-xref>.
+        </p>
+
+        <emu-table id="table-messageformatcontext-record"><figure><figcaption>Table 2: Record returned by CreateMessageContext</figcaption>
+          
+          <table class="real-table">
+            <thead>
+              <tr>
+                <th>Field Name</th>
+                <th>Value Type</th>
+                <th>Description</th>
+              </tr>
+            </thead>
+            <tbody><tr>
+              <td><var class="field">[[LocalVariables]]</var></td>
+              <td>Object</td>
+              <td>
+                Cache for local variables, which may be resolved during the formatting.
+                The values in the cache are Objects, each of which will have either <var class="field">[[MessageValue]]</var>, <var class="field">[[ResolvedValue]]</var>, or <var class="field">[[UnresolvedDeclaration]]</var> internal slots.
+              </td>
+            </tr>
+            <tr>
+              <td><var class="field">[[MessageFormat]]</var></td>
+              <td>Intl.MessageFormat</td>
+              <td>The MessageFormat instance on which the formatting is taking place.</td>
+            </tr>
+            <tr>
+              <td><var class="field">[[OnError]]</var></td>
+              <td>Function object or <emu-val>undefined</emu-val>.</td>
+              <td>The <var>onError</var> argument of the formatter call.</td>
+            </tr>
+            <tr>
+              <td><var class="field">[[Values]]</var></td>
+              <td>Object</td>
+              <td>The <var>values</var> argument of the formatter call.</td>
+            </tr>
+          </tbody></table>
+        </figure></emu-table>
+      </emu-clause>
+    </emu-clause>
 
-      <emu-alg><ol><li>Assert: <var>completionRecord</var> is a Completion Record.</li><li>Assert: <var>completionRecord</var> is an abrupt completion.</li><li>Let <var>error</var> be <var>completionRecord</var>.<var class="field">[[Value]]</var>.</li><li>If <var>onError</var> is not <emu-val>undefined</emu-val>, then<ol><li>Perform ?&nbsp;Call(<var>onError</var>, <emu-val>undefined</emu-val>, « <var>error</var>&nbsp;»).</li></ol></li><li>Else if an appropriate notification mechanism exists, then<ol><li>Issue a warning for <var>error</var>.</li></ol></li></ol></emu-alg>
+    <emu-clause id="sec-resolvemessage" type="abstract operation" aoid="ResolveMessage">
+      <h1><span class="secnum">1.5.4</span> ResolveMessage ( <var>ctx</var> )</h1>
+      <p>The abstract operation ResolveMessage takes argument <var>ctx</var> (a <emu-xref href="#messageformatcontext-record" id="_ref_24"><a href="#messageformatcontext-record">MessageFormatContext Record</a></emu-xref>) and returns a List of Strings and Objects. It resolves a message into a List of Strings and Objects with either <var class="field">[[MessageMarkup]]</var> or <var class="field">[[MessageValue]]</var> internal slots. It performs the following steps when called:</p>
+
+      <emu-alg><ol><li>Let <var>result</var> be an empty List.</li><li>Let <var>pattern</var> be ?&nbsp;<emu-xref aoid="SelectPattern" id="_ref_25"><a href="#sec-selectpattern">SelectPattern</a></emu-xref>(<var>ctx</var>).</li><li>For each element <var>el</var> of <var>pattern</var>,<ol><li>If <var>el</var> is a String, then<ol><li>Append <var>el</var> to <var>result</var>.</li></ol></li><li>Else,<ol><li>Let <var>elType</var> be ?&nbsp;Get(<var>el</var>, <emu-val>"type"</emu-val>).</li><li>If <var>elType</var> is <emu-val>"markup"</emu-val>, then<ol><li>Let <var>res</var> be OrdinaryObjectCreate(<emu-val>null</emu-val>, « <var class="field">[[MessageMarkup]]</var>&nbsp;»).</li><li>Set <var>res</var>.<var class="field">[[MessageMarkup]]</var> to <var>el</var>.</li></ol></li><li>Else,<ol><li>Assert: <var>elType</var> is <emu-val>"expression"</emu-val>.</li><li>Let <var>res</var> be <emu-xref aoid="ResolveExpression" id="_ref_26"><a href="#sec-resolveexpression">ResolveExpression</a></emu-xref>(<var>ctx</var>, <var>el</var>).</li></ol></li><li>Append <var>res</var> to <var>result</var>.</li></ol></li></ol></li><li>Return <var>result</var>.</li></ol></emu-alg>
+
+      <emu-clause id="sec-selectpattern" type="abstract operation" aoid="SelectPattern">
+        <h1><span class="secnum">1.5.4.1</span> SelectPattern ( <var>ctx</var> )</h1>
+        <p>The abstract operation SelectPattern takes argument <var>ctx</var> (a <emu-xref href="#messageformatcontext-record" id="_ref_27"><a href="#messageformatcontext-record">MessageFormatContext Record</a></emu-xref>) and returns a List of Strings and Objects with an internal slot <var class="field">[[MessageValue]]</var>. It selects the pattern to format from the message data model. It performs the following steps when called:</p>
+
+        <emu-alg><ol><li>Let <var>msgData</var> be <var>ctx</var>.<var class="field">[[MessageFormat]]</var>.<var class="field">[[MessageData]]</var>.</li><li>Let <var>msgType</var> be ?&nbsp;Get(<var>msgData</var>, <emu-val>"type"</emu-val>).</li><li>If <var>msgType</var> is <emu-val>"message"</emu-val>, then<ol><li>Let <var>pattern</var> be ?&nbsp;Get(<var>msgData</var>, <emu-val>"pattern"</emu-val>).</li></ol></li><li>Else,<ol><li>Assert: <var>msgType</var> is <emu-val>"select"</emu-val>.</li><li>Let <var>selectorsData</var> be ?&nbsp;Get(<var>msgData</var>, <emu-val>"selectors"</emu-val>).</li><li>Let <var>selectorExpressions</var> be ?&nbsp;CreateListFromArrayLike(<var>selectorsData</var>, « Object&nbsp;»).</li><li>Let <var>selectors</var> be an empty List of Object and Null values.</li><li>For each element <var>selExp</var> of <var>selectorExpressions</var>,<ol><li>Let <var>sel</var> be <emu-xref aoid="ResolveExpression" id="_ref_28"><a href="#sec-resolveexpression">ResolveExpression</a></emu-xref>(<var>ctx</var>, <var>selExp</var>).</li><li>Let <var>selectKey</var> be ?&nbsp;Get(<var>sel</var>.<var class="field">[[MessageValue]]</var>, <emu-val>"selectKey"</emu-val>).</li><li>If IsCallable(<var>selectKey</var>) is <emu-val>true</emu-val>, then<ol><li>Append <var>sel</var>.<var class="field">[[MessageValue]]</var> to <var>selectors</var>.</li></ol></li><li>Else,<ol><li>Let <var>error</var> be ThrowCompletion(<emu-val>TypeError</emu-val>).</li><li>Perform ?&nbsp;<emu-xref aoid="HandleMessageFormatError" id="_ref_29"><a href="#sec-handlemessageformaterror">HandleMessageFormatError</a></emu-xref>(<var>ctx</var>, <var>error</var>).</li><li>Append <emu-val>null</emu-val> to <var>selectors</var>.</li></ol></li></ol></li><li>Let <var>variantsArray</var> be ?&nbsp;Get(<var>msgData</var>, <emu-val>"variants"</emu-val>).</li><li>Let <var>variants</var> be ?&nbsp;CreateListFromArrayLike(<var>variantsArray</var>, « Object&nbsp;»).</li><li>Let <var>selectedVariant</var> be ?&nbsp;<emu-xref aoid="SelectVariant" id="_ref_30"><a href="#sec-selectvariant">SelectVariant</a></emu-xref>(<var>ctx</var>, <var>selectors</var>, <var>variants</var>).</li></ol></li><li>Return ?&nbsp;CreateListFromArrayLike(<var>pattern</var>, « String, Object&nbsp;»).</li></ol></emu-alg>
+      </emu-clause>
+
+      <emu-clause id="sec-selectvariant" type="implementation-defined abstract operation" aoid="SelectVariant">
+        <h1><span class="secnum">1.5.4.2</span> SelectVariant ( <var>ctx</var>, <var>selectors</var>, <var>variants</var> )</h1>
+        <p>The implementation-defined abstract operation SelectVariant takes arguments <var>ctx</var> (a <emu-xref href="#messageformatcontext-record" id="_ref_31"><a href="#messageformatcontext-record">MessageFormatContext Record</a></emu-xref>), <var>selectors</var> (a List of Object and Null values), and <var>variants</var> (a List of Objects) and returns an Object.</p>
+            <p>
+              It applies the variant selection method defined by
+              the "Resolve Preferences", "Filter Variants", and "Sort Variants" steps of the
+              <a href="https://github.com/unicode-org/message-format-wg/blob/main/spec/formatting.md#pattern-selection">Pattern Selection</a>
+              section of the Unicode MessageFormat 2.0 specification.
+            </p>
+
+            <p>
+              For the selection, Null values in <var>selectors</var> indicate selectors for which selection will always fail.
+              If any errors are encountered during the selection,
+              the <emu-xref aoid="HandleMessageFormatError" id="_ref_32"><a href="#sec-handlemessageformaterror">HandleMessageFormatError</a></emu-xref> abstract operation must be called
+              with <var>ctx</var> and an abrupt Completion Record containing an Error.
+            </p>
+
+            <p>
+              The value returned by this operation must be an Object matching the JSON Schema definition of a message pattern:
+              <a href="https://github.com/unicode-org/message-format-wg/blob/main/spec/data-model/message.json#/$defs/pattern">
+                https://github.com/unicode-org/message-format-wg/blob/main/spec/data-model/message.json#/$defs/pattern
+              </a>.
+            </p>
+          
+      </emu-clause>
     </emu-clause>
 
-    <emu-clause id="sec-messagefallbackpart" type="abstract operation" aoid="MessageFallbackPart">
-      <h1><span class="secnum">1.5.4</span> MessageFallbackPart ( <var>mv</var> )</h1>
-      <p>The abstract operation MessageFallbackPart takes argument <var>mv</var> (an Object) and returns an Object. It gets the fallback formatted part representation of a MessageValue It performs the following steps when called:</p>
+    <emu-clause id="sec-resolveexpression" type="abstract operation" aoid="ResolveExpression">
+      <h1><span class="secnum">1.5.5</span> ResolveExpression ( <var>ctx</var>, <var>expression</var> )</h1>
+      <p>The abstract operation ResolveExpression takes arguments <var>ctx</var> (a <emu-xref href="#messageformatcontext-record" id="_ref_33"><a href="#messageformatcontext-record">MessageFormatContext Record</a></emu-xref>) and <var>expression</var> (an Object) and returns an Object with an internal slot <var class="field">[[MessageValue]]</var>. It resolves the value of an expression for selection and formatting. It performs the following steps when called:</p>
 
-      <emu-alg><ol><li>Let <var>result</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Let <var>source</var> be <emu-xref aoid="MessageValueSource" id="_ref_14"><a href="#sec-messagevaluesource">MessageValueSource</a></emu-xref>(<var>mv</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>result</var>, <emu-val>"type"</emu-val>, <emu-val>"fallback"</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>result</var>, <emu-val>"source"</emu-val>, <var>source</var>).</li><li>Return <var>result</var>.</li></ol></emu-alg>
-    </emu-clause>
+      <emu-alg><ol><li>Let <var>source</var> be ?&nbsp;<emu-xref aoid="GetSource" id="_ref_34"><a href="#sec-getsource">GetSource</a></emu-xref>(<var>ctx</var>, <var>expression</var>).</li><li>Let <var>arg</var> be ?&nbsp;Get(<var>expression</var>, <emu-val>"arg"</emu-val>).</li><li>If <var>arg</var> is <emu-val>undefined</emu-val>, then<ol><li>Let <var>resArg</var> be <emu-val>undefined</emu-val>.</li></ol></li><li>Else,<ol><li>Let <var>resArg</var> be <emu-xref aoid="ResolveValue" id="_ref_35"><a href="#sec-resolvevalue">ResolveValue</a></emu-xref>(<var>ctx</var>, <var>arg</var>).</li><li>If <var>resArg</var> has a <var class="field">[[MessageFallback]]</var> internal slot, return <var>resArg</var>.</li></ol></li><li>Let <var>annotation</var> be ?&nbsp;Get(<var>expression</var>, <emu-val>"annotation"</emu-val>).</li><li>If <var>annotation</var> is <emu-val>undefined</emu-val>, then<ol><li>Assert: <var>resArg</var> is not <emu-val>undefined</emu-val>.</li><li>If <var>resArg</var> is an Object and <var>resArg</var> has a <var class="field">[[MessageValue]]</var> internal slot, then<ol><li>Return <var>resArg</var>.</li></ol></li><li>Else if <var>resArg</var> is a Number or <var>resArg</var> is a BigInt, then<ol><li>Set <var>annotation</var> to OrdinaryObjectCreate(<emu-val>null</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>annotation</var>, <emu-val>"type"</emu-val>, <emu-val>"function"</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>annotation</var>, <emu-val>"name"</emu-val>, <emu-val>"number"</emu-val>).</li></ol></li><li>Else if <var>resArg</var> is a String, then<ol><li>Set <var>annotation</var> to OrdinaryObjectCreate(<emu-val>null</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>annotation</var>, <emu-val>"type"</emu-val>, <emu-val>"function"</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>annotation</var>, <emu-val>"name"</emu-val>, <emu-val>"string"</emu-val>).</li></ol></li><li>Else,<ol><li>Return <emu-xref aoid="ResolveUnknown" id="_ref_36"><a href="#sec-resolveunknown">ResolveUnknown</a></emu-xref>(<var>source</var>, <var>resArg</var>).</li></ol></li></ol></li><li>If ?&nbsp;Get(<var>annotation</var>, <emu-val>"type"</emu-val>) is not <emu-val>"function"</emu-val>, then<ol><li>Let <var>error</var> be ThrowCompletion(<emu-val>ReferenceError</emu-val>).</li><li>Perform ?&nbsp;<emu-xref aoid="HandleMessageFormatError" id="_ref_37"><a href="#sec-handlemessageformaterror">HandleMessageFormatError</a></emu-xref>(<var>ctx</var>, <var>error</var>).</li><li>Return <emu-xref aoid="ResolveFallback" id="_ref_38"><a href="#sec-resolvefallback">ResolveFallback</a></emu-xref>(<var>source</var>).</li></ol></li><li>Return <emu-xref aoid="ResolveFunction" id="_ref_39"><a href="#sec-resolvefunction">ResolveFunction</a></emu-xref>(<var>ctx</var>, <var>source</var>, <var>resArg</var>, <var>annotation</var>).</li></ol></emu-alg>
 
-    <emu-clause id="sec-messagefallbackstring" type="abstract operation" aoid="MessageFallbackString">
-      <h1><span class="secnum">1.5.5</span> MessageFallbackString ( <var>mv</var> )</h1>
-      <p>The abstract operation MessageFallbackString takes argument <var>mv</var> (an Object) and returns a String. It gets the fallback formatted string representation of a MessageValue It performs the following steps when called:</p>
+      <emu-clause id="sec-resolvefunction" type="abstract operation" aoid="ResolveFunction">
+        <h1><span class="secnum">1.5.5.1</span> ResolveFunction ( <var>ctx</var>, <var>source</var>, <var>resArg</var>, <var>annotation</var> )</h1>
+        <p>The abstract operation ResolveFunction takes arguments <var>ctx</var> (a <emu-xref href="#messageformatcontext-record" id="_ref_40"><a href="#messageformatcontext-record">MessageFormatContext Record</a></emu-xref>), <var>source</var> (a String), <var>resArg</var> (an Object or undefined), and <var>annotation</var> (an Object) and returns an Object with an internal slot <var class="field">[[MessageValue]]</var>. It resolves the value of an expression with a function annotation. It performs the following steps when called:</p>
 
-      <emu-alg><ol><li>Let <var>source</var> be <emu-xref aoid="MessageValueSource" id="_ref_15"><a href="#sec-messagevaluesource">MessageValueSource</a></emu-xref>(<var>mv</var>).</li><li>Let <var>result</var> be the string-concatenation of <emu-val>"{"</emu-val>, <var>source</var>, and <emu-val>"}"</emu-val>.</li><li>Return <var>result</var>.</li></ol></emu-alg>
-    </emu-clause>
+        <emu-alg><ol><li>Let <var>name</var> be ?&nbsp;Get(<var>annotation</var>, <emu-val>"name"</emu-val>).</li><li>Let <var>function</var> be ?&nbsp;Get(<var>ctx</var>.<var class="field">[[MessageFormat]]</var>.<var class="field">[[Functions]]</var>, <var>name</var>).</li><li>If IsCallable(<var>function</var>) is <emu-val>false</emu-val>, then<ol><li>Let <var>error</var> be ThrowCompletion(<emu-val>ReferenceError</emu-val>).</li><li>Perform ?&nbsp;<emu-xref aoid="HandleMessageFormatError" id="_ref_41"><a href="#sec-handlemessageformaterror">HandleMessageFormatError</a></emu-xref>(<var>ctx</var>, <var>error</var>).</li><li>Return <emu-xref aoid="ResolveFallback" id="_ref_42"><a href="#sec-resolvefallback">ResolveFallback</a></emu-xref>(<var>source</var>).</li></ol></li><li>Let <var>funcCtx</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>funcCtx</var>, <emu-val>"locale"</emu-val>, <var>ctx</var>.<var class="field">[[MessageFormat]]</var>.<var class="field">[[RequestedLocales]]</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>funcCtx</var>, <emu-val>"localeMatcher"</emu-val>, <var>ctx</var>.<var class="field">[[MessageFormat]]</var>.<var class="field">[[LocaleMatcher]]</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>funcCtx</var>, <emu-val>"source"</emu-val>, <var>source</var>).</li><li>Let <var>options</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Let <var>optArray</var> be ?&nbsp;Get(<var>annotation</var>, <emu-val>"options"</emu-val>).</li><li>If <var>optArray</var> is not <emu-val>undefined</emu-val>, then<ol><li>Let <var>optList</var> be ?&nbsp;CreateListFromArrayLike(<var>optArray</var>).</li><li>For each element <var>opt</var> of <var>optList</var>,<ol><li>Let <var>optName</var> be ?&nbsp;Get(<var>opt</var>, <emu-val>"name"</emu-val>).</li><li>Let <var>optValue</var> be ?&nbsp;Get(<var>opt</var>, <emu-val>"value"</emu-val>).</li><li>Let <var>resValue</var> be <emu-xref aoid="ResolveValue" id="_ref_43"><a href="#sec-resolvevalue">ResolveValue</a></emu-xref>(<var>ctx</var>, <var>optValue</var>).</li><li>If <var>resValue</var> is an Object, then<ol><li>If <var>resValue</var> has a <var class="field">[[MessageFallback]]</var> internal slot, then<ol><li>Set <var>resValue</var> to <emu-val>undefined</emu-val>.</li></ol></li><li>Else if <var>resValue</var> has a <var class="field">[[MessageValue]]</var> internal slot, then<ol><li>Set <var>resValue</var> to <var>resValue</var>.<var class="field">[[MessageValue]]</var>.</li></ol></li></ol></li><li>Perform ?&nbsp;CreateDataPropertyOrThrow(<var>options</var>, <var>optName</var>, <var>resValue</var>).</li></ol></li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>part</var>, <emu-val>"options"</emu-val>, <var>resOptions</var>).</li></ol></li><li>Let <var>funcArgs</var> be « <var>funcCtx</var>, <var>options</var>&nbsp;».</li><li>If <var>resArg</var> is an Object and <var>resArg</var> has a <var class="field">[[MessageValue]]</var> internal slot, then<ol><li>Set <var>resArg</var> to <var>resArg</var>.<var class="field">[[MessageValue]]</var>.</li></ol></li><li>If <var>resArg</var> is not <emu-val>undefined</emu-val>, then<ol><li>Append <var>resArg</var> to <var>funcArgs</var>.</li></ol></li><li>Let <var>funcRes</var> be Completion(Call(<var>function</var>, <emu-val>undefined</emu-val>, <var>funcArgs</var>)).</li><li>If <var>funcRes</var> is a normal completion, then<ol><li>Let <var>result</var> be OrdinaryObjectCreate(<emu-val>null</emu-val>, « <var class="field">[[MessageValue]]</var>&nbsp;»).</li><li>Set <var>result</var>.<var class="field">[[MessageValue]]</var> to <var>funcRes</var>.<var class="field">[[Value]]</var>.</li><li>Return <var>result</var>.</li></ol></li><li>Else,<ol><li>Perform ?&nbsp;<emu-xref aoid="HandleMessageFormatError" id="_ref_44"><a href="#sec-handlemessageformaterror">HandleMessageFormatError</a></emu-xref>(<var>ctx</var>, <var>funcRes</var>).</li><li>Return <emu-xref aoid="ResolveFallback" id="_ref_45"><a href="#sec-resolvefallback">ResolveFallback</a></emu-xref>(<var>source</var>).</li></ol></li></ol></emu-alg>
+      </emu-clause>
 
-    <emu-clause id="sec-messagevaluesource" type="abstract operation" aoid="MessageValueSource">
-      <h1><span class="secnum">1.5.6</span> MessageValueSource ( <var>mv</var> )</h1>
-      <p>The abstract operation MessageValueSource takes argument <var>mv</var> (an Object) and returns a String. 
-          It gets the source string representation of a MessageValue,
-          which should be always available.
-          On any error, return the Unicode replacement character � instead.
-         It performs the following steps when called:</p>
+      <emu-clause id="sec-resolveunknown" type="abstract operation" aoid="ResolveUnknown">
+        <h1><span class="secnum">1.5.5.2</span> ResolveUnknown ( <var>source</var>, <var>value</var> )</h1>
+        <p>The abstract operation ResolveUnknown takes arguments <var>source</var> (a String) and <var>value</var> (an ECMAScript language value) and returns an Object with an internal slot <var class="field">[[MessageValue]]</var>. It resolves an unknown value. It performs the following steps when called:</p>
 
-      <emu-alg><ol><li>Let <var>source</var> be Completion(Get(<var>mv</var>, <emu-val>"source"</emu-val>)).</li><li>If <var>source</var> is a normal completion, then<ol><li>Let <var>str</var> be <var>source</var>.<var class="field">[[Value]]</var>.</li><li>If <var>str</var> is a String, then<ol><li>Return <var>str</var>.</li></ol></li></ol></li><li>Return <emu-val>"\uFFFD"</emu-val>.</li></ol></emu-alg>
+        <emu-alg><ol><li>Let <var>toPartsClosure</var> be a new Abstract Closure with no parameters that captures <var>source</var> and <var>value</var> and performs the following steps when called:<ol><li>Let <var>part</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>part</var>, <emu-val>"type"</emu-val>, <emu-val>"unknown"</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>part</var>, <emu-val>"source"</emu-val>, <var>source</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>part</var>, <emu-val>"value"</emu-val>, <var>value</var>).</li><li>Return CreateArrayFromList(« <var>part</var>&nbsp;»).</li></ol></li><li>Let <var>toParts</var> be CreateBuiltinFunction(<var>toPartsClosure</var>, <emu-val>0</emu-val>, <emu-val>"toParts"</emu-val>, «&nbsp;»).</li><li>Let <var>toStringClosure</var> be a new Abstract Closure with no parameters that captures <var>value</var> and performs the following steps when called:<ol><li>Return ?&nbsp;ToString(<var>value</var>).</li></ol></li><li>Let <var>toString</var> be CreateBuiltinFunction(<var>toStringClosure</var>, <emu-val>0</emu-val>, <emu-val>"toString"</emu-val>, «&nbsp;»).</li><li>Let <var>valueOfClosure</var> be a new Abstract Closure with no parameters that captures <var>value</var> and performs the following steps when called:<ol><li>Return <var>value</var>.</li></ol></li><li>Let <var>valueOf</var> be CreateBuiltinFunction(<var>valueOfClosure</var>, <emu-val>0</emu-val>, <emu-val>"valueOf"</emu-val>, «&nbsp;»).</li><li>Let <var>mv</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"type"</emu-val>, <emu-val>"unknown"</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"source"</emu-val>, <var>source</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"locale"</emu-val>, <emu-val>"und"</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"toParts"</emu-val>, <var>toParts</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"toString"</emu-val>, <var>toString</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"valueOf"</emu-val>, <var>valueOf</var>).</li><li>Let <var>unknown</var> be OrdinaryObjectCreate(<emu-val>null</emu-val>, « <var class="field">[[MessageValue]]</var>&nbsp;»).</li><li>Set <var>unknown</var>.<var class="field">[[MessageValue]]</var> to <var>mv</var>.</li><li>Return <var>unknown</var>.</li></ol></emu-alg>
+      </emu-clause>
     </emu-clause>
 
-    <emu-clause id="sec-resolveexpression" type="abstract operation" aoid="ResolveExpression">
-      <h1><span class="secnum">1.5.7</span> ResolveExpression ( <var>mf</var>, <var>values</var>, <var>onError</var>, <var>expression</var> )</h1>
-      <p>The abstract operation ResolveExpression takes arguments <var>mf</var> (an Object), <var>values</var> (an Object or undefined), <var>onError</var> (a Function or undefined), and <var>expression</var> (an Object) and returns an Object. It resolves the value of an expression for selection and formatting. It performs the following steps when called:</p>
+    <emu-clause id="sec-formatmarkuppart" type="abstract operation" aoid="FormatMarkupPart">
+      <h1><span class="secnum">1.5.6</span> FormatMarkupPart ( <var>ctx</var>, <var>markup</var> )</h1>
+      <p>The abstract operation FormatMarkupPart takes arguments <var>ctx</var> (a <emu-xref href="#messageformatcontext-record" id="_ref_46"><a href="#messageformatcontext-record">MessageFormatContext Record</a></emu-xref>) and <var>markup</var> (an Object) and returns an Object. It resolves the formatted part value of a markup placeholder. It performs the following steps when called:</p>
 
-      <emu-alg><ol><li>...TODO</li></ol></emu-alg>
+      <emu-alg><ol><li>Let <var>kind</var> be ?&nbsp;Get(<var>markup</var>, <emu-val>"kind"</emu-val>).</li><li>Let <var>name</var> be ?&nbsp;Get(<var>markup</var>, <emu-val>"name"</emu-val>).</li><li>Let <var>options</var> be ?&nbsp;Get(<var>markup</var>, <emu-val>"options"</emu-val>).</li><li>Let <var>part</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>part</var>, <emu-val>"type"</emu-val>, <emu-val>"markup"</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>part</var>, <emu-val>"kind"</emu-val>, <var>kind</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>part</var>, <emu-val>"name"</emu-val>, <var>name</var>).</li><li>If <var>kind</var> is not <emu-val>"close"</emu-val> and <var>options</var> is not <emu-val>undefined</emu-val>, then<ol><li>Let <var>len</var> be ?&nbsp;LengthOfArrayLike(<var>options</var>).</li><li>If <var>len</var> &gt; 0, then<ol><li>Let <var>opts</var> be ?&nbsp;CreateListFromArrayLike(<var>options</var>).</li><li>Let <var>resOptions</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>For each element <var>opt</var> of <var>opts</var>,<ol><li>Let <var>optName</var> be ?&nbsp;Get(<var>opt</var>, <emu-val>"name"</emu-val>).</li><li>Let <var>optValue</var> be ?&nbsp;Get(<var>opt</var>, <emu-val>"value"</emu-val>).</li><li>Let <var>resValue</var> be <emu-xref aoid="ResolveValue" id="_ref_47"><a href="#sec-resolvevalue">ResolveValue</a></emu-xref>(<var>ctx</var>, <var>optValue</var>).</li><li>If <var>resValue</var> is an Object, then<ol><li>If <var>resValue</var> has a <var class="field">[[MessageFallback]]</var> internal slot, then<ol><li>Set <var>resValue</var> to <emu-val>undefined</emu-val>.</li></ol></li><li>Else,<ol><li>Let <var>valueOf</var> be ?&nbsp;Get(<var>resValue</var>, <emu-val>"valueOf"</emu-val>).</li><li>If IsCallable(<var>valueOf</var>) is <emu-val>true</emu-val>, then<ol><li>Let <var>valueOfResult</var> be Completion(Call(<var>valueOf</var>, <var>resValue</var>)).</li><li>If <var>valueOfResult</var> is a normal completion, then<ol><li>Set <var>resValue</var> to <var>valueOfResult</var>.<var class="field">[[Value]]</var>.</li></ol></li><li>Else,<ol><li>Perform ?&nbsp;<emu-xref aoid="HandleMessageFormatError" id="_ref_48"><a href="#sec-handlemessageformaterror">HandleMessageFormatError</a></emu-xref>(<var>ctx</var>, <var>valueOfResult</var>).</li><li>Set <var>resValue</var> to <emu-val>undefined</emu-val>.</li></ol></li></ol></li></ol></li></ol></li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>resOptions</var>, <var>optName</var>, <var>resValue</var>).</li></ol></li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>part</var>, <emu-val>"options"</emu-val>, <var>resOptions</var>).</li></ol></li></ol></li><li>Return CreateArrayFromList(« <var>part</var>&nbsp;»).</li></ol></emu-alg>
     </emu-clause>
 
-    <emu-clause id="sec-resolvemessage" type="abstract operation" aoid="ResolveMessage">
-      <h1><span class="secnum">1.5.8</span> ResolveMessage ( <var>mf</var>, <var>values</var>, <var>onError</var> )</h1>
-      <p>The abstract operation ResolveMessage takes arguments <var>mf</var> (an Object), <var>values</var> (an Object or undefined), and <var>onError</var> (a Function or undefined) and returns a List of Objects. It resolves a message during formatting into a List of MessageValue Objects. It performs the following steps when called:</p>
+    <emu-clause id="sec-getsource" type="abstract operation" aoid="GetSource">
+      <h1><span class="secnum">1.5.7</span> GetSource ( <var>ctx</var>, <var>value</var> )</h1>
+      <p>The abstract operation GetSource takes arguments <var>ctx</var> (a <emu-xref href="#messageformatcontext-record" id="_ref_49"><a href="#messageformatcontext-record">MessageFormatContext Record</a></emu-xref>) and <var>value</var> (an Object) and returns a String. Determines the "source" value for a data model Object. It performs the following steps when called:</p>
+
+      <emu-alg><ol><li>Let <var>type</var> be ?&nbsp;Get(<var>value</var>, <emu-val>"type"</emu-val>).</li><li>If <var>type</var> is <emu-val>"literal"</emu-val>, then<ol><li>Let <var>strValue</var> be ?&nbsp;Get(<var>value</var>, <emu-val>"value"</emu-val>).</li><li>Modify <var>strValue</var> such that all <emu-val>"\"</emu-val> characters are replaced with <emu-val>"\"</emu-val>.</li><li>Modify <var>strValue</var> such that all <emu-val>"|"</emu-val> characters are replaced with <emu-val>"|"</emu-val>.</li><li>Return the string-concatenation of <emu-val>"|"</emu-val>, <var>strValue</var>, and <emu-val>"|"</emu-val>.</li></ol></li><li>If <var>type</var> is <emu-val>"variable"</emu-val>, then<ol><li>Let <var>name</var> be ?&nbsp;Get(<var>value</var>, <emu-val>"name"</emu-val>).</li><li>Let <var>local</var> be !&nbsp;Get(<var>ctx</var>.<var class="field">[[LocalVariables]]</var>, <var>name</var>).</li><li>If <var>local</var> has an <var class="field">[[UnresolvedDeclaration]]</var> internal slot, then<ol><li>Let <var>decl</var> be <var>local</var>.<var class="field">[[UnresolvedDeclaration]]</var>.</li><li>If ?&nbsp;Get(<var>decl</var>, <emu-val>"type"</emu-val>) is <emu-val>"local"</emu-val>, then<ol><li>Let <var>declValue</var> be ?&nbsp;Get(<var>decl</var>, <emu-val>"value"</emu-val>).</li><li>Return ?&nbsp;<emu-xref aoid="GetSource" id="_ref_50"><a href="#sec-getsource">GetSource</a></emu-xref>(<var>ctx</var>, <var>declValue</var>).</li></ol></li></ol></li><li>Else if <var>local</var> has a <var class="field">[[MessageValue]]</var> internal slot, then<ol><li>Return <emu-xref aoid="MessageValueSource" id="_ref_51"><a href="#sec-messagevaluesource">MessageValueSource</a></emu-xref>(<var>local</var>.<var class="field">[[MessageValue]]</var>).</li></ol></li><li>Else,<ol><li>Assert: <var>local</var> has a <var class="field">[[ResolvedName]]</var> internal slot.</li><li>Assert: <var>local</var> has a <var class="field">[[ResolvedValue]]</var> internal slot.</li><li>Set <var>name</var> to <var>local</var>.<var class="field">[[ResolvedName]]</var>.</li></ol></li><li>Return the string-concatenation of <emu-val>"$"</emu-val> and <var>name</var>.</li></ol></li><li>If <var>type</var> is <emu-val>"markup"</emu-val>, then<ol><li>Let <var>kind</var> be ?&nbsp;Get(<var>value</var>, <emu-val>"kind"</emu-val>).</li><li>Let <var>name</var> be ?&nbsp;Get(<var>value</var>, <emu-val>"name"</emu-val>).</li><li>If <var>kind</var> is <emu-val>"open"</emu-val>, return the string-concatenation of <emu-val>"#"</emu-val> and <var>name</var>.</li><li>If <var>kind</var> is <emu-val>"standalone"</emu-val>, return the string-concatenation of <emu-val>"#"</emu-val>, <var>name</var>, and <emu-val>"/"</emu-val>.</li><li>If <var>kind</var> is <emu-val>"close"</emu-val>, return the string-concatenation of <emu-val>"/"</emu-val> and <var>name</var>.</li></ol></li><li>If <var>type</var> is <emu-val>"function"</emu-val>, then<ol><li>Let <var>name</var> be ?&nbsp;Get(<var>value</var>, <emu-val>"name"</emu-val>).</li><li>Return the string-concatenation of <emu-val>":"</emu-val> and <var>name</var>.</li></ol></li><li>If <var>type</var> is <emu-val>"unsupported-annotation"</emu-val>, then<ol><li>Return ?&nbsp;Get(<var>value</var>, <emu-val>"sigil"</emu-val>).</li></ol></li><li>If <var>type</var> is <emu-val>"expression"</emu-val>, then<ol><li>Let <var>arg</var> be ?&nbsp;Get(<var>value</var>, <emu-val>"arg"</emu-val>).</li><li>If <var>arg</var> is not <emu-val>undefined</emu-val>, return ?&nbsp;<emu-xref aoid="GetSource" id="_ref_52"><a href="#sec-getsource">GetSource</a></emu-xref>(<var>ctx</var>, <var>arg</var>).</li><li>Let <var>annotation</var> be ?&nbsp;Get(<var>value</var>, <emu-val>"annotation"</emu-val>).</li><li>If <var>annotation</var> is not <emu-val>undefined</emu-val>, return ?&nbsp;<emu-xref aoid="GetSource" id="_ref_53"><a href="#sec-getsource">GetSource</a></emu-xref>(<var>ctx</var>, <var>annotation</var>).</li></ol></li><li>Return <emu-val>"\uFFFD"</emu-val>.</li></ol></emu-alg>
+
+      <emu-clause id="sec-messagevaluesource" type="abstract operation" aoid="MessageValueSource">
+        <h1><span class="secnum">1.5.7.1</span> MessageValueSource ( <var>mv</var> )</h1>
+        <p>The abstract operation MessageValueSource takes argument <var>mv</var> (an Object) and returns a String. 
+            It gets the source string representation of a resolved message value,
+            which should be always available.
+            On any error, return the Unicode replacement character � instead.
+           It performs the following steps when called:</p>
 
-      <emu-alg><ol><li>Let <var>result</var> be an empty List.</li><li>Let <var>pattern</var> be ?&nbsp;<emu-xref aoid="SelectPattern" id="_ref_16"><a href="#sec-selectpattern">SelectPattern</a></emu-xref>(<var>mf</var>, <var>values</var>, <var>onError</var>).</li><li>For each element <var>el</var> of <var>pattern</var>,<ol><li>If <var>el</var> is a String, then<ol><li>Append <var>el</var> to <var>result</var>.</li></ol></li><li>Else,<ol><li>Let <var>mv</var> be <emu-xref aoid="ResolveExpression" id="_ref_17"><a href="#sec-resolveexpression">ResolveExpression</a></emu-xref>(<var>mf</var>, <var>values</var>, <var>onError</var>, <var>el</var>).</li><li>Append <var>mv</var> to <var>result</var>.</li></ol></li></ol></li><li>Return <var>result</var>.</li></ol></emu-alg>
+        <emu-alg><ol><li>Let <var>source</var> be Completion(Get(<var>mv</var>, <emu-val>"source"</emu-val>)).</li><li>If <var>source</var> is a normal completion, then<ol><li>Let <var>str</var> be <var>source</var>.<var class="field">[[Value]]</var>.</li><li>If <var>str</var> is a String, then<ol><li>Return <var>str</var>.</li></ol></li></ol></li><li>Return <emu-val>"\uFFFD"</emu-val>.</li></ol></emu-alg>
+      </emu-clause>
     </emu-clause>
 
-    <emu-clause id="sec-selectpattern" type="abstract operation" aoid="SelectPattern">
-      <h1><span class="secnum">1.5.9</span> SelectPattern ( <var>mf</var>, <var>values</var>, <var>onError</var> )</h1>
-      <p>The abstract operation SelectPattern takes arguments <var>mf</var> (an Object), <var>values</var> (an Object or undefined), and <var>onError</var> (a Function or undefined) and returns a List of Strings and Objects. It selects the pattern to format from the message data model. It performs the following steps when called:</p>
+    <emu-clause id="sec-handlemessageformaterror" type="abstract operation" aoid="HandleMessageFormatError">
+      <h1><span class="secnum">1.5.8</span> HandleMessageFormatError ( <var>ctx</var>, <var>completionRecord</var> )</h1>
+      <p>The abstract operation HandleMessageFormatError takes arguments <var>ctx</var> (a <emu-xref href="#messageformatcontext-record" id="_ref_54"><a href="#messageformatcontext-record">MessageFormatContext Record</a></emu-xref>) and <var>completionRecord</var> (a Completion Record). It handles errors during formatting. It performs the following steps when called:</p>
 
-      <emu-alg><ol><li>Let <var>msgData</var> be <var>mf</var>.<var class="field">[[MessageData]]</var>.</li><li>Let <var>msgType</var> be ?&nbsp;Get(<var>msgData</var>, <emu-val>"type"</emu-val>).</li><li>Assert: <var>msgType</var> is a String.</li><li>If <var>msgType</var> is <emu-val>"message"</emu-val>, then<ol><li>Let <var>pattern</var> be ?&nbsp;Get(<var>msgData</var>, <emu-val>"pattern"</emu-val>).</li></ol></li><li>Else,<ol><li>Let <var>selectorsData</var> be ?&nbsp;Get(<var>msgData</var>, <emu-val>"selectors"</emu-val>).</li><li>Let <var>selectorExpressions</var> be ?&nbsp;CreateListFromArrayLike(<var>selectorsData</var>, « Object&nbsp;»).</li><li>Let <var>selectors</var> be an empty List of Object and Null values.</li><li>For each element <var>selExp</var> of <var>selectorExpressions</var>,<ol><li>Let <var>sel</var> be <emu-xref aoid="ResolveExpression" id="_ref_18"><a href="#sec-resolveexpression">ResolveExpression</a></emu-xref>(<var>mf</var>, <var>values</var>, <var>onError</var>, <var>selExp</var>).</li><li>Let <var>selectKeys</var> be ?&nbsp;Get(<var>sel</var>, <emu-val>"selectKeys"</emu-val>).</li><li>If IsCallable(<var>selectKeys</var>) is <emu-val>true</emu-val>, then<ol><li>Append <var>sel</var> to <var>selectors</var>.</li></ol></li><li>Else,<ol><li>Let <var>errorCompletion</var> be ThrowCompletion(<emu-val>TypeError</emu-val>).</li><li>Perform ?&nbsp;<emu-xref aoid="HandleMessageFormatError" id="_ref_19"><a href="#sec-handlemessageformaterror">HandleMessageFormatError</a></emu-xref>(<var>onError</var>, <var>errorCompletion</var>).</li><li>Append <emu-val>null</emu-val> to <var>selectors</var>.</li></ol></li></ol></li><li>Let <var>variantsArray</var> be ?&nbsp;Get(<var>msgData</var>, <emu-val>"variants"</emu-val>).</li><li>Let <var>variants</var> be ?&nbsp;CreateListFromArrayLike(<var>variantsArray</var>, « Object&nbsp;»).</li><li>Let <var>selectedVariant</var> be ?&nbsp;<emu-xref aoid="SelectVariant" id="_ref_20"><a href="#sec-selectvariant">SelectVariant</a></emu-xref>(<var>selectors</var>, <var>variants</var>, <var>onError</var>).</li></ol></li><li>Let <var>patternBody</var> be ?&nbsp;Get(<var>pattern</var>, <emu-val>"body"</emu-val>).</li><li>Return ?&nbsp;CreateListFromArrayLike(<var>patternBody</var>, « String, Object&nbsp;»).</li></ol></emu-alg>
+      <emu-alg><ol><li>Assert: <var>completionRecord</var> is a Completion Record.</li><li>Assert: <var>completionRecord</var> is an abrupt completion.</li><li>Let <var>onError</var> be <var>ctx</var>.<var class="field">[[OnError]]</var>.</li><li>Let <var>error</var> be <var>completionRecord</var>.<var class="field">[[Value]]</var>.</li><li>If <var>onError</var> is not <emu-val>undefined</emu-val>, then<ol><li>Perform ?&nbsp;Call(<var>onError</var>, <emu-val>undefined</emu-val>, « <var>error</var>&nbsp;»).</li></ol></li><li>Else if an appropriate notification mechanism exists, then<ol><li>Issue a warning for <var>error</var>.</li></ol></li></ol></emu-alg>
     </emu-clause>
 
-    <emu-clause id="sec-selectvariant" type="implementation-defined abstract operation" aoid="SelectVariant">
-      <h1><span class="secnum">1.5.10</span> SelectVariant ( <var>selectors</var>, <var>variants</var>, <var>onError</var> )</h1>
-      <p>The implementation-defined abstract operation SelectVariant takes arguments <var>selectors</var> (a List of Object and Null values), <var>variants</var> (a List of Objects), and <var>onError</var> (a Function or undefined) and returns an Object.</p>
-          <p>
-            It applies the variant selection method defined by
-            the "Resolve Preferences", "Filter Variants", and "Sort Variants" steps of the
-            <a href="https://github.com/unicode-org/message-format-wg/blob/main/spec/formatting.md#pattern-selection">Pattern Selection</a>
-            section of the Unicode MessageFormat 2.0 specification.
-          </p>
+    <emu-clause id="sec-resolvefallback" type="abstract operation" aoid="ResolveFallback">
+      <h1><span class="secnum">1.5.9</span> ResolveFallback ( <var>source</var> )</h1>
+      <p>The abstract operation ResolveFallback takes argument <var>source</var> (a String) and returns an Object with internal slots <var class="field">[[MessageFallback]]</var> and <var class="field">[[MessageValue]]</var>. It resolves a fallback value. It performs the following steps when called:</p>
 
-          <p>
-            For the selection, Null values in <var>selectors</var> indicate selectors for which selection will always fail.
-            If any errors are encountered during the selection,
-            the <emu-xref aoid="HandleMessageFormatError" id="_ref_21"><a href="#sec-handlemessageformaterror">HandleMessageFormatError</a></emu-xref> abstract operation must be called
-            with <var>onError</var> and an abrupt Completion Record containing an Error.
-          </p>
+      <emu-alg><ol><li>Let <var>toPartsClosure</var> be a new Abstract Closure with no parameters that captures <var>source</var> and performs the following steps when called:<ol><li>Let <var>part</var> be <emu-xref aoid="MessageFallbackPart" id="_ref_55"><a href="#sec-messagefallbackpart">MessageFallbackPart</a></emu-xref>(<var>source</var>).</li><li>Return CreateArrayFromList(« <var>part</var>&nbsp;»).</li></ol></li><li>Let <var>toParts</var> be CreateBuiltinFunction(<var>toPartsClosure</var>, <emu-val>0</emu-val>, <emu-val>"toParts"</emu-val>, «&nbsp;»).</li><li>Let <var>toStringClosure</var> be a new Abstract Closure with no parameters that captures <var>source</var> and performs the following steps when called:<ol><li>Return <emu-xref aoid="MessageFallbackString" id="_ref_56"><a href="#sec-messagefallbackstring">MessageFallbackString</a></emu-xref>(<var>source</var>).</li></ol></li><li>Let <var>toString</var> be CreateBuiltinFunction(<var>toStringClosure</var>, <emu-val>0</emu-val>, <emu-val>"toString"</emu-val>, «&nbsp;»).</li><li>Let <var>mv</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"source"</emu-val>, <var>source</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"toParts"</emu-val>, <var>toParts</var>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>mv</var>, <emu-val>"toString"</emu-val>, <var>toString</var>).</li><li>Let <var>fallback</var> be OrdinaryObjectCreate(<emu-val>null</emu-val>, « <var class="field">[[MessageFallback]]</var>, <var class="field">[[MessageValue]]</var>&nbsp;»).</li><li>Set <var>fallback</var>.<var class="field">[[MessageValue]]</var> to <var>mv</var>.</li><li>Return <var>fallback</var>.</li></ol></emu-alg>
 
-          <p>
-            The value returned by this operation must be an Object matching the JSON Schema definition of a message pattern:
-            <a href="https://github.com/unicode-org/message-format-wg/blob/main/spec/data-model/message.json#/$defs/pattern">
-              https://github.com/unicode-org/message-format-wg/blob/main/spec/data-model/message.json#/$defs/pattern
-            </a>.
-          </p>
-        
+      <emu-clause id="sec-messagefallbackpart" type="abstract operation" aoid="MessageFallbackPart">
+        <h1><span class="secnum">1.5.9.1</span> MessageFallbackPart ( <var>source</var> )</h1>
+        <p>The abstract operation MessageFallbackPart takes argument <var>source</var> (a String) and returns an Object. It gets the fallback formatted part representation. It performs the following steps when called:</p>
+
+        <emu-alg><ol><li>Let <var>result</var> be OrdinaryObjectCreate(%Object.prototype%).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>result</var>, <emu-val>"type"</emu-val>, <emu-val>"fallback"</emu-val>).</li><li>Perform !&nbsp;CreateDataPropertyOrThrow(<var>result</var>, <emu-val>"source"</emu-val>, <var>source</var>).</li><li>Return <var>result</var>.</li></ol></emu-alg>
+      </emu-clause>
+
+      <emu-clause id="sec-messagefallbackstring" type="abstract operation" aoid="MessageFallbackString">
+        <h1><span class="secnum">1.5.9.2</span> MessageFallbackString ( <var>source</var> )</h1>
+        <p>The abstract operation MessageFallbackString takes argument <var>source</var> (a String) and returns a String. It gets the fallback formatted string representation. It performs the following steps when called:</p>
+
+        <emu-alg><ol><li>Return the string-concatenation of <emu-val>"{"</emu-val>, <var>source</var>, and <emu-val>"}"</emu-val>.</li></ol></emu-alg>
+      </emu-clause>
+    </emu-clause>
+
+    <emu-clause id="sec-resolvevalue" type="abstract operation" aoid="ResolveValue">
+      <h1><span class="secnum">1.5.10</span> ResolveValue ( <var>ctx</var>, <var>value</var> )</h1>
+      <p>The abstract operation ResolveValue takes arguments <var>ctx</var> (a <emu-xref href="#messageformatcontext-record" id="_ref_57"><a href="#messageformatcontext-record">MessageFormatContext Record</a></emu-xref>) and <var>value</var> (an Object) and returns an ECMAScript language value. 
+          It resolves the value of a literal or variable reference.
+          For literals, the returned value is always a String.
+          For variable references, the returned value may be any ECMAScript language value.
+          For unresolved variable references, the returned value is an Object with an internal slot <var class="field">[[MessageFallback]]</var>.
+         It performs the following steps when called:</p>
+
+      <emu-alg><ol><li>Let <var>type</var> be ?&nbsp;Get(<var>value</var>, <emu-val>"type"</emu-val>).</li><li>If <var>type</var> is <emu-val>"literal"</emu-val>, then<ol><li>Return ?&nbsp;Get(<var>value</var>, <emu-val>"value"</emu-val>).</li></ol></li><li>Assert: <var>type</var> is <emu-val>"variable"</emu-val>.</li><li>Let <var>name</var> be ?&nbsp;Get(<var>value</var>, <emu-val>"name"</emu-val>).</li><li>Let <var>localVars</var> be <var>ctx</var>.<var class="field">[[LocalVariables]]</var>.</li><li>Let <var>var</var> be !&nbsp;Get(<var>localVars</var>, <var>name</var>).</li><li>If <var>var</var> is <emu-val>undefined</emu-val>, then<ol><li>Set <var>var</var> to ?&nbsp;Get(<var>ctx</var>.<var class="field">[[Values]]</var>, <var>name</var>).</li><li>If <var>var</var> is <emu-val>undefined</emu-val>, then<ol><li>Let <var>error</var> be ThrowCompletion(<emu-val>ReferenceError</emu-val>).</li><li>Perform ?&nbsp;<emu-xref aoid="HandleMessageFormatError" id="_ref_58"><a href="#sec-handlemessageformaterror">HandleMessageFormatError</a></emu-xref>(<var>ctx</var>, <var>error</var>).</li><li>Let <var>source</var> be ?&nbsp;<emu-xref aoid="GetSource" id="_ref_59"><a href="#sec-getsource">GetSource</a></emu-xref>(<var>value</var>).</li><li>Set <var>var</var> to <emu-xref aoid="ResolveFallback" id="_ref_60"><a href="#sec-resolvefallback">ResolveFallback</a></emu-xref>(<var>source</var>).</li><li>Perform !&nbsp;Set(<var>localVars</var>, <var>name</var>, <var>var</var>).</li></ol></li><li>Else,<ol><li>Let <var>resolved</var> be OrdinaryObjectCreate(<emu-val>null</emu-val>, « <var class="field">[[ResolvedName]]</var>, <var class="field">[[ResolvedValue]]</var>&nbsp;»).</li><li>Set <var>resolved</var>.<var class="field">[[ResolvedName]]</var> to <var>name</var>.</li><li>Set <var>resolved</var>.<var class="field">[[ResolvedValue]]</var> to <var>var</var>.</li><li>Perform !&nbsp;Set(<var>localVars</var>, <var>name</var>, <var>resolved</var>).</li></ol></li></ol></li><li>Else,<ol><li>Assert: <var>var</var> is an Object.</li><li>If <var>var</var> has a <var class="field">[[ResolvedValue]]</var> internal slot, then<ol><li>Set <var>var</var> to <var>var</var>.<var class="field">[[ResolvedValue]]</var>.</li></ol></li><li>Else if <var>var</var> has an <var class="field">[[UnresolvedDeclaration]]</var> internal slot, then<ol><li>Let <var>decl</var> be <var>var</var>.<var class="field">[[UnresolvedDeclaration]]</var>.</li><li>Let <var>declType</var> be ?&nbsp;Get(<var>decl</var>, <emu-val>"type"</emu-val>).</li><li>If <var>declType</var> is <emu-val>"input"</emu-val>, then<ol><li>Let <var>expression</var> be ?&nbsp;Get(<var>decl</var>, <emu-val>"value"</emu-val>).</li><li>Perform !&nbsp;Set(<var>localVars</var>, <var>name</var>, <emu-val>undefined</emu-val>).</li><li>Set <var>var</var> to ?&nbsp;<emu-xref aoid="ResolveExpression" id="_ref_61"><a href="#sec-resolveexpression">ResolveExpression</a></emu-xref>(<var>ctx</var>, <var>expression</var>).</li></ol></li><li>Else if <var>declType</var> is <emu-val>"local"</emu-val>, then<ol><li>Let <var>expression</var> be ?&nbsp;Get(<var>decl</var>, <emu-val>"value"</emu-val>).</li><li>Set <var>var</var> to ?&nbsp;<emu-xref aoid="ResolveExpression" id="_ref_62"><a href="#sec-resolveexpression">ResolveExpression</a></emu-xref>(<var>ctx</var>, <var>expression</var>).</li></ol></li><li>Else,<ol><li>Let <var>error</var> be ThrowCompletion(<emu-val>ReferenceError</emu-val>).</li><li>Perform ?&nbsp;<emu-xref aoid="HandleMessageFormatError" id="_ref_63"><a href="#sec-handlemessageformaterror">HandleMessageFormatError</a></emu-xref>(<var>ctx</var>, <var>error</var>).</li><li>Let <var>source</var> be ?&nbsp;<emu-xref aoid="GetSource" id="_ref_64"><a href="#sec-getsource">GetSource</a></emu-xref>(<var>value</var>).</li><li>Set <var>var</var> to <emu-xref aoid="ResolveFallback" id="_ref_65"><a href="#sec-resolvefallback">ResolveFallback</a></emu-xref>(<var>source</var>).</li></ol></li><li>Perform !&nbsp;Set(<var>localVars</var>, <var>name</var>, <var>var</var>).</li></ol></li></ol></li><li>Return <var>var</var>.</li></ol></emu-alg>
     </emu-clause>
   </emu-clause>
 </emu-clause><emu-annex id="sec-copyright-and-software-license">
       <h1><span class="secnum">A</span> Copyright &amp; Software License</h1>
       
       <h2>Copyright Notice</h2>
-      <p>© 2023 Eemeli Aro</p>
+      <p>© 2024 Eemeli Aro</p>
 
       <h2>Software License</h2>
       <p>All Software contained in this document ("Software") is protected by copyright and is being made available under the "BSD License", included below. This Software may be subject to third party rights (rights from parties other than Ecma International), including patent rights, and no licenses under such third party rights are granted under this license even if the third party concerned is a member of Ecma International. SEE THE ECMA CODE OF CONDUCT IN PATENT MATTERS AVAILABLE AT <a href="https://ecma-international.org/memento/codeofconduct.htm">https://ecma-international.org/memento/codeofconduct.htm</a> FOR INFORMATION REGARDING THE LICENSING OF PATENT CLAIMS THAT ARE REQUIRED TO IMPLEMENT ECMA INTERNATIONAL STANDARDS.</p>
diff --git a/spec.emu b/spec.emu
index 52cc9ba..0c4c660 100644
--- a/spec.emu
+++ b/spec.emu
@@ -137,19 +137,23 @@ contributors: Eemeli Aro
       <emu-alg>
         1. Let _mf_ be the *this* value.
         1. Perform ? RequireInternalSlot(_mf_, [[InitializedMessageFormat]]).
-        1. Let _msg_ be ? ResolveMessage(_mf_, _values_, _onError_).
+        1. Let _ctx_ be ? CreateMessageFormatContext(_mf_, _values_, _onError_).
+        1. Let _msg_ be ? ResolveMessage(_ctx_).
         1. Let _result_ be an empty String.
-        1. For each element _mv_ of _msg_, do
-           1. If _mv_ is a String, then
-              1. Let _stringValue_ be _mv_.
-           1. Else,
+        1. For each element _el_ of _msg_, do
+           1. If _el_ is a String, then
+              1. Let _stringValue_ be _el_.
+           1. Else if _el_ has a [[MessageValue]] internal slot, then
+              1. Let _mv_ be _el_.[[MessageValue]].
+              1. Assert: _mv_ is an Object.
               1. Let _toString_ be ? Get(_mv_, *"toString"*).
               1. Let _toStringResult_ be Completion(Call(_toString_, _mv_)).
               1. If _toStringResult_ is a normal completion, then
                  1. Let _stringValue_ be _toStringResult_.[[Value]].
               1. Else,
-                 1. Perform ? HandleMessageFormatError(_onError_, _stringResult_).
-                 1. Let _stringValue_ be MessageFallbackString(_mv_).
+                 1. Perform ? HandleMessageFormatError(_ctx_, _stringResult_).
+                 1. Let _source_ be MessageValueSource(_mv_).
+                 1. Let _stringValue_ be MessageFallbackString(_source_).
            1. Set _result_ to the string-concatenation of _result_ and _stringValue_.
         1. Return _result_.
       </emu-alg>
@@ -166,23 +170,30 @@ contributors: Eemeli Aro
       <emu-alg>
         1. Let _mf_ be the *this* value.
         1. Perform ? RequireInternalSlot(_mf_, [[InitializedMessageFormat]]).
-        1. Let _msg_ be ? ResolveMessage(_mf_, _values_, _onError_).
+        1. Let _ctx_ be ? CreateMessageFormatContext(_mf_, _values_, _onError_).
+        1. Let _msg_ be ? ResolveMessage(_ctx_).
         1. Let _result_ be an empty List of Objects.
         1. For each element _mv_ of _msg_, do
-           1. If _mv_ is a String, then
+           1. If _el_ is a String, then
               1. Let _textPart_ be OrdinaryObjectCreate(%Object.prototype%).
               1. Perform ! CreateDataPropertyOrThrow(_textPart_, *"type"*, *"text"*).
-              1. Perform ! CreateDataPropertyOrThrow(_textPart_, *"value"*, _mv_).
+              1. Perform ! CreateDataPropertyOrThrow(_textPart_, *"value"*, _el_).
               1. Append _textPart_ to _result_.
+           1. Else if _el_ has a [[MessageMarkup]] internal slot, then
+              1. Let _markup_ be ? FormatMarkupPart(_ctx_, _el_.[[MessageMarkup]]).
+              1. Append _markup_ to _result_
            1. Else,
+              1. Let _mv_ be _el_.[[MessageValue]].
+              1. Assert: _mv_ is an Object.
               1. Let _toParts_ be ? Get(_mv_, *"toParts"*).
               1. Let _partResult_ be Completion(Call(_toParts_, _mv_)).
               1. If _partResult_ is a normal completion, then
                  1. Let _parts_ be _partResult_.[[Value]].
-                 1. For each _part_ of _parts_, append _part_ to _result_.
+                 1. For each element _part_ of _parts_, append _part_ to _result_.
               1. Else,
-                 1. Perform ? HandleMessageFormatError(_onError_, _partResult_).
-                 1. Let _fallbackPart_ be MessageFallbackPart(_mv_).
+                 1. Perform ? HandleMessageFormatError(_ctx_, _partResult_).
+                 1. Let _source_ be MessageValueSource(_mv_).
+                 1. Let _fallbackPart_ be MessageFallbackPart(_source_).
                  1. Append _fallbackPart_ to _result_.
         1. Return CreateArrayFromList(_result_).
       </emu-alg>
@@ -260,13 +271,17 @@ contributors: Eemeli Aro
         [[LocaleMatcher]] is one of the String values *"lookup"* or *"best fit"*,
         identifying the locale matcher used.
       </li>
-      <li>[[MessageData]] is an Object ...TODO</li>
+      <li>
+        [[MessageData]] is an Object conforming to the
+        <a href="https://github.com/unicode-org/message-format-wg/blob/main/spec/data-model/message.json">JSON Schema definition</a>
+        of the Unicode MessageFormat 2.0 specification.
+      </li>
       <li>
         [[RequestedLocales]] is a List of String values
         with the canonicalized language tags of the requested locales
         to use for message formatting.
       </li>
-      <li>[[Functions]] is an Object ...TODO</li>
+      <li>[[Functions]] is an Object with function object values.</li>
     </ul>
   </emu-clause>
 
@@ -299,7 +314,7 @@ contributors: Eemeli Aro
       <h1>
         GetMessageFunctions (
           _userFunctions_: an Object or undefined,
-        ): a Record
+        ): an Object
       </h1>
       <dl class="header">
         <dt>description</dt>
@@ -307,214 +322,757 @@ contributors: Eemeli Aro
       </dl>
 
       <emu-alg>
-        1. ...TODO
+        1. Let _numberSteps_ be the algorithm steps defined in <emu-xref href="#sec-messageformat-numberfunctions"></emu-xref>.
+        1. Let _number_ be CreateBuiltinFunction(_numberSteps_, *3*, *"number"*, « »).
+        1. Let _stringSteps_ be the algorithm steps defined in <emu-xref href="#sec-messageformat-stringfunctions"></emu-xref>.
+        1. Let _string_ be CreateBuiltinFunction(_stringSteps_, *3*, *"string"*, « »).
+        1. Let _functions_ be OrdinaryObjectCreate(%Object.prototype%).
+        1. Perform ! CreateDataPropertyOrThrow(_functions_, *"number"*, _number_).
+        1. Perform ! CreateDataPropertyOrThrow(_functions_, *"string"*, _string_).
+        1. For each String _name_ of ? EnumerableOwnProperties(_userFunctions_, ~key~),
+           1. Let _func_ be ? Get(_userFunctions_, _name_).
+           1. If IsCallable(_func_) is *true*, then
+              1. Perform ! CreateDataPropertyOrThrow(_functions_, _name_, _func_).
+           1. Else,
+              1. Throw a *TypeError* exception.
+        1. Return _functions_.
       </emu-alg>
+
+      <emu-clause id="sec-messageformat-numberfunctions">
+        <h1>MessageFormat Number Functions</h1>
+        <p>
+          A MessageFormat number function is an anonymous built-in function.
+        </p>
+        <p>
+          When a MessageFormat number function is called with arguments _funcCtx_ (an Object), _options_ (an Object), and _input_ (an ECMAScript language value), the following steps are taken:
+        </p>
+
+        <emu-alg>
+          1. Let _locale_ be ! Get(_funcCtx_, *"locale"*).
+          1. Let _localeMatcher_ be ! Get(_funcCtx_, *"localeMatcher"*).
+          1. Let _source_ be ! Get(_funcCtx_, *"source"*).
+          1. Let _opts_ be OrdinaryObjectCreate(%Object.prototype%).
+          1. Perform ! CreateDataPropertyOrThrow(_opt_, *"localeMatcher"*, _localeMatcher_).
+          1. If _input_ is a String, then
+             1. Set _input_ to ? Call(JSON.parse, %JSON%, « _input_ »).
+          1. Else if _input_ is an Object, then
+             1. Let _valueOf_ be ? Get(_input_, *"valueOf"*).
+             1. If IsCallable(_valueOf_) is *true*, then
+                1. Let _inputOptions_ be ? Get(_input_, *"options"*).
+                1. Perform ? Call(Object.assign, *undefined*, « _opts_, _inputOptions_ »).
+                1. Set _input_ to ? Call(_valueOf_, _input_).
+          1. If _input_ is not a Number and _input_ is not a BigInt, throw a *TypeError* exception.
+          1. Let _numberOptions_ be « *"minimumIntegerDigits"*, *"minimumFractionDigits"*, *"maximumFractionDigits"*, *"minimumSignificantDigits"*, *"maximumSignificantDigits"*, *"roundingIncrement"* ».
+          1. Let _booleanOptions_ be « *"useGrouping"* ».
+          1. Let _select_ be *"cardinal"*.
+          1. For each String _optName_ of ? EnumerableOwnProperties(_options_, ~key~),
+             1. If _optName_ is not *"localeMatcher"* and _optName_ is not *"type"*, then
+                1. If _optValue_ is an Object, then
+                   1. Let _optValueOf_ be ? Get(_optValue_, *"valueOf"*).
+                   1. If IsCallable(_optValueOf_) is *true*, then
+                      1. Set _optValue__ to ? Call(_optValueOf_, _optValue_).
+                1. If _optName_ is *"select"*, then
+                   1. If _optValue_ is *"ordinal"* or _optValue_ is *"exact"*, then
+                      1. Set _select_ to _optValue_
+                   1. Else if _optValue_ is not *"plural"*, then
+                      1. Throw a *RangeError* exception.
+                1. Else,
+                   1. If _optValue_ is a String, then
+                      1. If _numberOptions_ contains _optName_, then
+                         1. Set _optValue_ to ToNumber(_optValue_).
+                      1. Else if _booleanOptions_ contains _optName_, then
+                         1. If _optValue_ is *"true"*, then
+                            1. Set _optValue_ to *true*.
+                         1. Else if _optValue_ is *"false"*, then
+                            1. Set _optValue_ to *false*.
+                   1. Perform ? Set(_opts_, _optName_, _optValue_, *true*).
+          1. Let _numberFormat_ be ? Construct(%Intl.NumberFormat%, « _locale_, _opts_ »).
+          1. If _select_ is *"exact"*, then
+             1. Perform ? _opts_.[[Delete]](*"type"*).
+             1. Let _pluralRules_ be *undefined*.
+          1. Else,
+             1. Perform ? Set(_opts_, *"type"*, _select_, *true*).
+             1. Let _pluralRules_ be ? Construct(%Intl.PluralRules%, « _locale_, _opts_ »).
+          1. Let _selectKeyClosure_ be a new Abstract Closure with parameters (_keys_) that captures _input_ and _pluralRules_ and performs the following steps when called:
+             1. Let _keyList_ be ? CreateListFromArrayLike(_keys_, « String »).
+             1. Let _str_ be ? ToString(_input_).
+             1. If _keyList_ contains _str_, return _str_.
+             1. If _pluralRules_ is not *undefined*, then
+                1. Let _category_ be ? Call(Intl.PluralRules.prototype.select, _pluralRules_, « _input_ »).
+                1. If _keyList_ contains _category_, return _category_.
+             1. Return *null*.
+          1. Let _selectKey_ be CreateBuiltinFunction(_selectKeyClosure_, *1*, *"selectKey"*, « »).
+          1. Let _toPartsClosure_ be a new Abstract Closure with no parameters that captures _input_, _source_, and _numberFormat_ and performs the following steps when called:
+             1. Let _parts_ be ? Call(Intl.NumberFormat.prototype.formatToParts, _nf_, « _input_ »).
+             1. Let _result_ be OrdinaryObjectCreate(%Object.prototype%).
+             1. Perform ! CreateDataPropertyOrThrow(_result_, *"type"*, *"number"*).
+             1. Perform ! CreateDataPropertyOrThrow(_result_, *"source"*, _source_).
+             1. Perform ! CreateDataPropertyOrThrow(_result_, *"locale"*, _numberFormat_.[[Locale]]).
+             1. Perform ! CreateDataPropertyOrThrow(_result_, *"parts"*, _parts_).
+             1. Return CreateArrayFromList(« _result_ »).
+          1. Let _toParts_ be CreateBuiltinFunction(_toPartsClosure_, *0*, *"toParts"*, « »).
+          1. Let _toStringClosure_ be a new Abstract Closure with no parameters that captures _input_ and _numberFormat_ and performs the following steps when called:
+             1. Return ? Call(Intl.NumberFormat.prototype.format, _nf_, « _input_ »).
+          1. Let _toString_ be CreateBuiltinFunction(_toStringClosure_, *0*, *"toString"*, « »).
+          1. Let _valueOfClosure_ be a new Abstract Closure with no parameters that captures _input_ and performs the following steps when called:
+             1. Return _input_.
+          1. Let _valueOf_ be CreateBuiltinFunction(_valueOfClosure_, *0*, *"valueOf"*, « »).
+          1. Let _mv_ be OrdinaryObjectCreate(%Object.prototype%).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"type"*, *"number"*).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"source"*, _source_).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"locale"*, _numberFormat_.[[Locale]]).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"options"*, _opts_).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"selectKey"*, _selectKey_).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"toParts"*, _toParts_).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"toString"*, _toString_).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"valueOf"*, _valueOf_).
+          1. Return _mv_.
+        </emu-alg>
+
+        <p>
+          The *"length"* property of a MessageFormat number function is *3*.
+        </p>
+      </emu-clause>
+
+      <emu-clause id="sec-messageformat-stringfunctions">
+        <h1>MessageFormat String Functions</h1>
+        <p>
+          A MessageFormat string function is an anonymous built-in function.
+        </p>
+        <p>
+          When a MessageFormat string function is called with arguments _funcCtx_ (an Object), _options_ (an Object), and _input_ (an ECMAScript language value), the following steps are taken:
+        </p>
+
+        <emu-alg>
+          1. Let _str_ be ? ToString(_input_).
+          1. Let _selectKeyClosure_ be a new Abstract Closure with parameters (_keys_) that captures _str_ and performs the following steps when called:
+             1. Let _keyList_ be ? CreateListFromArrayLike(_keys_, « String »).
+             1. If _keyList_ contains _str_, return _str_.
+             1. Else, return *null*.
+          1. Let _selectKey_ be CreateBuiltinFunction(_selectKeyClosure_, *1*, *"selectKey"*, « »).
+          1. Let _toPartsClosure_ be a new Abstract Closure with no parameters that captures _funcCtx_ and _str_ and performs the following steps when called:
+             1. Let _source_ be ! Get(_funcCtx_, *"source"*).
+             1. Let _locale_ be ! Get(_funcCtx_, *"locale"*).
+             1. Let _locale0_ be ! Get(_locale_, *"0"*).
+             1. Let _result_ be OrdinaryObjectCreate(%Object.prototype%).
+             1. Perform ! CreateDataPropertyOrThrow(_result_, *"type"*, *"string"*).
+             1. Perform ! CreateDataPropertyOrThrow(_result_, *"source"*, _source_).
+             1. Perform ! CreateDataPropertyOrThrow(_result_, *"locale"*, _locale0_).
+             1. Perform ! CreateDataPropertyOrThrow(_result_, *"value"*, _str_).
+             1. Return CreateArrayFromList(« _result_ »).
+          1. Let _toParts_ be CreateBuiltinFunction(_toPartsClosure_, *0*, *"toParts"*, « »).
+          1. Let _toStringClosure_ be a new Abstract Closure with no parameters that captures _str_ and performs the following steps when called:
+             1. Return _str_.
+          1. Let _toString_ be CreateBuiltinFunction(_toStringClosure_, *0*, *"toString"*, « »).
+          1. Let _valueOf_ be CreateBuiltinFunction(_toStringClosure_, *0*, *"valueOf"*, « »).
+          1. Let _mv_ be OrdinaryObjectCreate(%Object.prototype%).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"type"*, *"number"*).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"source"*, _source_).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"locale"*, _numberFormat_.[[Locale]]).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"options"*, _opts_).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"selectKey"*, _selectKey_).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"toParts"*, _toParts_).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"toString"*, _toString_).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"valueOf"*, _valueOf_).
+          1. Return _mv_.
+        </emu-alg>
+
+        <p>
+          The *"length"* property of a MessageFormat string function is *3*.
+        </p>
+      </emu-clause>
     </emu-clause>
 
-    <emu-clause id="sec-handlemessageformaterror" type="abstract operation">
+    <emu-clause id="sec-createmessageformatcontext" type="abstract operation">
       <h1>
-        HandleMessageFormatError(
-          _onError_: a Function or undefined,
-          _completionRecord_: a Completion Record,
-        )
+        CreateMessageFormatContext (
+          _mf_: an Object,
+          _values_: an Object or undefined,
+          _onError_: a Function or undefined
+        ): a MessageFormatContext Record
       </h1>
       <dl class="header">
         <dt>description</dt>
-        <dd>It handles errors during formatting.</dd>
+        <dd>It initializes the MessageFormatContext Record used for pattern selection and formatting.</dd>
       </dl>
 
       <emu-alg>
-        1. Assert: _completionRecord_ is a Completion Record.
-        1. Assert: _completionRecord_ is an abrupt completion.
-        1. Let _error_ be _completionRecord_.[[Value]].
-        1. If _onError_ is not *undefined*, then
-           1. Perform ? Call(_onError_, *undefined*, &laquo; _error_ &raquo;).
-        1. Else if an appropriate notification mechanism exists, then
-           1. Issue a warning for _error_.
+        1. Let _localVars_ be OrdinaryObjectCreate(*null*).
+        1. Let _msgData_ be _mf_.[[MessageData]].
+        1. Let _declArray_ be ? Get(_msgData_, *"declarations"*).
+        1. Let _declList_ be ? CreateListFromArrayLike(_declArray_).
+        1. For each element _decl_ of _declList_,
+           1. Let _declName_ be ? Get(_decl_, *"name"*).
+           1. Let _declValue_ be OrdinaryObjectCreate(*null*, « [[UnresolvedDeclaration]] »).
+           1. Set _declValue_.[[UnresolvedDeclaration]] to _decl_.
+           1. Perform ? Set(_localVars_, _declName_, _declValue_, *true*).
+        1. Let _ctx_ be a new Record.
+        1. Set _ctx_.[[LocalVariables]] to _localVars_.
+        1. Set _ctx_.[[MessageFormat]] to _mf_.
+        1. Set _ctx_.[[OnError]] to _onError_.
+        1. Set _ctx_.[[Values]] to ? GetOptionsObject(_values_).
+        1. Return _ctx_.
       </emu-alg>
+
+      <emu-clause id="sec-messagecontextrecord">
+        <h1>MessageFormatContext Records</h1>
+        <p>
+          A <dfn id="messageformatcontext-record">MessageFormatContext Record</dfn> is used to hold the data required during the formatting of a message.
+          It has the fields defined in <emu-xref href="#table-messageformatcontext-record"></emu-xref>.
+        </p>
+
+        <emu-table id="table-messageformatcontext-record">
+          <emu-caption>Record returned by CreateMessageContext</emu-caption>
+          <table class="real-table">
+            <thead>
+              <tr>
+                <th>Field Name</th>
+                <th>Value Type</th>
+                <th>Description</th>
+              </tr>
+            </thead>
+            <tr>
+              <td>[[LocalVariables]]</td>
+              <td>Object</td>
+              <td>
+                Cache for local variables, which may be resolved during the formatting.
+                The values in the cache are Objects, each of which will have either [[MessageValue]], [[ResolvedValue]], or [[UnresolvedDeclaration]] internal slots.
+              </td>
+            </tr>
+            <tr>
+              <td>[[MessageFormat]]</td>
+              <td>Intl.MessageFormat</td>
+              <td>The MessageFormat instance on which the formatting is taking place.</td>
+            </tr>
+            <tr>
+              <td>[[OnError]]</td>
+              <td>Function object or *undefined*.</td>
+              <td>The _onError_ argument of the formatter call.</td>
+            </tr>
+            <tr>
+              <td>[[Values]]</td>
+              <td>Object</td>
+              <td>The _values_ argument of the formatter call.</td>
+            </tr>
+          </table>
+        </emu-table>
+      </emu-clause>
     </emu-clause>
 
-    <emu-clause id="sec-messagefallbackpart" type="abstract operation">
+    <emu-clause id="sec-resolvemessage" type="abstract operation">
       <h1>
-        MessageFallbackPart (
-          _mv_: an Object
-        ): an Object
+        ResolveMessage (
+          _ctx_: a MessageFormatContext Record
+        ): a List of Strings and Objects
       </h1>
       <dl class="header">
         <dt>description</dt>
-        <dd>It gets the fallback formatted part representation of a MessageValue</dd>
+        <dd>It resolves a message into a List of Strings and Objects with either [[MessageMarkup]] or [[MessageValue]] internal slots.</dd>
       </dl>
 
       <emu-alg>
-        1. Let _result_ be OrdinaryObjectCreate(%Object.prototype%).
-        1. Let _source_ be MessageValueSource(_mv_).
-        1. Perform ! CreateDataPropertyOrThrow(_result_, *"type"*, *"fallback"*).
-        1. Perform ! CreateDataPropertyOrThrow(_result_, *"source"*, _source_).
+        1. Let _result_ be an empty List.
+        1. Let _pattern_ be ? SelectPattern(_ctx_).
+        1. For each element _el_ of _pattern_,
+           1. If _el_ is a String, then
+              1. Append _el_ to _result_.
+           1. Else,
+              1. Let _elType_ be ? Get(_el_, *"type"*).
+              1. If _elType_ is *"markup"*, then
+                1. Let _res_ be OrdinaryObjectCreate(*null*, « [[MessageMarkup]] »).
+                1. Set _res_.[[MessageMarkup]] to _el_.
+              1. Else,
+                1. Assert: _elType_ is *"expression"*.
+                1. Let _res_ be ResolveExpression(_ctx_, _el_).
+              1. Append _res_ to _result_.
         1. Return _result_.
       </emu-alg>
+
+      <emu-clause id="sec-selectpattern" type="abstract operation">
+        <h1>
+          SelectPattern (
+            _ctx_: a MessageFormatContext Record
+          ): a List of Strings and Objects with an internal slot [[MessageValue]]
+        </h1>
+        <dl class="header">
+          <dt>description</dt>
+          <dd>It selects the pattern to format from the message data model.</dd>
+        </dl>
+
+        <emu-alg>
+          1. Let _msgData_ be _ctx_.[[MessageFormat]].[[MessageData]].
+          1. Let _msgType_ be ? Get(_msgData_, *"type"*).
+          1. If _msgType_ is *"message"*, then
+             1. Let _pattern_ be ? Get(_msgData_, *"pattern"*).
+          1. Else,
+             1. Assert: _msgType_ is *"select"*.
+             1. Let _selectorsData_ be ? Get(_msgData_, *"selectors"*).
+             1. Let _selectorExpressions_ be ? CreateListFromArrayLike(_selectorsData_, &laquo; Object &raquo;).
+             1. Let _selectors_ be an empty List of Object and Null values.
+             1. For each element _selExp_ of _selectorExpressions_,
+                1. Let _sel_ be ResolveExpression(_ctx_, _selExp_).
+                1. Let _selectKey_ be ? Get(_sel_.[[MessageValue]], *"selectKey"*).
+                1. If IsCallable(_selectKey_) is *true*, then
+                   1. Append _sel_.[[MessageValue]] to _selectors_.
+                1. Else,
+                   1. Let _error_ be ThrowCompletion(*TypeError*).
+                   1. Perform ? HandleMessageFormatError(_ctx_, _error_).
+                   1. Append *null* to _selectors_.
+             1. Let _variantsArray_ be ? Get(_msgData_, *"variants"*).
+             1. Let _variants_ be ? CreateListFromArrayLike(_variantsArray_, &laquo; Object &raquo;).
+             1. Let _selectedVariant_ be ? SelectVariant(_ctx_, _selectors_, _variants_).
+          1. Return ? CreateListFromArrayLike(_pattern_, &laquo; String, Object &raquo;).
+        </emu-alg>
+      </emu-clause>
+
+      <emu-clause id="sec-selectvariant" type="implementation-defined abstract operation">
+        <h1>
+          SelectVariant (
+            _ctx_: a MessageFormatContext Record,
+            _selectors_: a List of Object and Null values,
+            _variants_: a List of Objects
+          ): an Object
+        </h1>
+        <dl class="header">
+          <dt>description</dt>
+          <dd>
+            <p>
+              It applies the variant selection method defined by
+              the "Resolve Preferences", "Filter Variants", and "Sort Variants" steps of the
+              <a href="https://github.com/unicode-org/message-format-wg/blob/main/spec/formatting.md#pattern-selection">Pattern Selection</a>
+              section of the Unicode MessageFormat 2.0 specification.
+            </p>
+
+            <p>
+              For the selection, Null values in _selectors_ indicate selectors for which selection will always fail.
+              If any errors are encountered during the selection,
+              the HandleMessageFormatError abstract operation must be called
+              with _ctx_ and an abrupt Completion Record containing an Error.
+            </p>
+
+            <p>
+              The value returned by this operation must be an Object matching the JSON Schema definition of a message pattern:
+              <a href="https://github.com/unicode-org/message-format-wg/blob/main/spec/data-model/message.json#/$defs/pattern">
+                https://github.com/unicode-org/message-format-wg/blob/main/spec/data-model/message.json#/$defs/pattern
+              </a>.
+            </p>
+          </dd>
+        </dl>
+      </emu-clause>
     </emu-clause>
 
-    <emu-clause id="sec-messagefallbackstring" type="abstract operation">
+    <emu-clause id="sec-resolveexpression" type="abstract operation">
       <h1>
-        MessageFallbackString (
-          _mv_: an Object
-        ): a String
+        ResolveExpression (
+          _ctx_: a MessageFormatContext Record,
+          _expression_: an Object,
+        ): an Object with an internal slot [[MessageValue]]
       </h1>
       <dl class="header">
         <dt>description</dt>
-        <dd>It gets the fallback formatted string representation of a MessageValue</dd>
+        <dd>It resolves the value of an expression for selection and formatting.</dd>
       </dl>
 
       <emu-alg>
-        1. Let _source_ be MessageValueSource(_mv_).
-        1. Let _result_ be the string-concatenation of *"{"*, _source_, and *"}"*.
-        1. Return _result_.
+        1. Let _source_ be ? GetSource(_ctx_, _expression_).
+        1. Let _arg_ be ? Get(_expression_, *"arg"*).
+        1. If _arg_ is *undefined*, then
+           1. Let _resArg_ be *undefined*.
+        1. Else,
+           1. Let _resArg_ be ResolveValue(_ctx_, _arg_).
+           1. If _resArg_ has a [[MessageFallback]] internal slot, return _resArg_.
+        1. Let _annotation_ be ? Get(_expression_, *"annotation"*).
+        1. If _annotation_ is *undefined*, then
+           1. Assert: _resArg_ is not *undefined*.
+           1. If _resArg_ is an Object and _resArg_ has a [[MessageValue]] internal slot, then
+              1. Return _resArg_.
+           1. Else if _resArg_ is a Number or _resArg_ is a BigInt, then
+              1. Set _annotation_ to OrdinaryObjectCreate(*null*).
+              1. Perform ! CreateDataPropertyOrThrow(_annotation_, *"type"*, *"function"*).
+              1. Perform ! CreateDataPropertyOrThrow(_annotation_, *"name"*, *"number"*).
+           1. Else if _resArg_ is a String, then
+              1. Set _annotation_ to OrdinaryObjectCreate(*null*).
+              1. Perform ! CreateDataPropertyOrThrow(_annotation_, *"type"*, *"function"*).
+              1. Perform ! CreateDataPropertyOrThrow(_annotation_, *"name"*, *"string"*).
+           1. Else,
+              1. Return ResolveUnknown(_source_, _resArg_).
+        1. If ? Get(_annotation_, *"type"*) is not *"function"*, then
+           1. Let _error_ be ThrowCompletion(*ReferenceError*).
+           1. Perform ? HandleMessageFormatError(_ctx_, _error_).
+           1. Return ResolveFallback(_source_).
+        1. Return ResolveFunction(_ctx_, _source_, _resArg_, _annotation_).
       </emu-alg>
+
+      <emu-clause id="sec-resolvefunction" type="abstract operation">
+        <h1>
+          ResolveFunction (
+            _ctx_: a MessageFormatContext Record,
+            _source_: a String,
+            _resArg_: an Object or undefined,
+            _annotation_: an Object,
+          ): an Object with an internal slot [[MessageValue]]
+        </h1>
+        <dl class="header">
+          <dt>description</dt>
+          <dd>It resolves the value of an expression with a function annotation.</dd>
+        </dl>
+
+        <emu-alg>
+          1. Let _name_ be ? Get(_annotation_, *"name"*).
+          1. Let _function_ be ? Get(_ctx_.[[MessageFormat]].[[Functions]], _name_).
+          1. If IsCallable(_function_) is *false*, then
+             1. Let _error_ be ThrowCompletion(*ReferenceError*).
+             1. Perform ? HandleMessageFormatError(_ctx_, _error_).
+             1. Return ResolveFallback(_source_).
+          1. Let _funcCtx_ be OrdinaryObjectCreate(%Object.prototype%).
+          1. Perform ! CreateDataPropertyOrThrow(_funcCtx_, *"locale"*, _ctx_.[[MessageFormat]].[[RequestedLocales]]).
+          1. Perform ! CreateDataPropertyOrThrow(_funcCtx_, *"localeMatcher"*, _ctx_.[[MessageFormat]].[[LocaleMatcher]]).
+          1. Perform ! CreateDataPropertyOrThrow(_funcCtx_, *"source"*, _source_).
+          1. Let _options_ be OrdinaryObjectCreate(%Object.prototype%).
+          1. Let _optArray_ be ? Get(_annotation_, *"options"*).
+          1. If _optArray_ is not *undefined*, then
+             1. Let _optList_ be ? CreateListFromArrayLike(_optArray_).
+             1. For each element _opt_ of _optList_,
+                1. Let _optName_ be ? Get(_opt_, *"name"*).
+                1. Let _optValue_ be ? Get(_opt_, *"value"*).
+                1. Let _resValue_ be ResolveValue(_ctx_, _optValue_).
+                1. If _resValue_ is an Object, then
+                   1. If _resValue_ has a [[MessageFallback]] internal slot, then
+                      1. Set _resValue_ to *undefined*.
+                   1. Else if _resValue_ has a [[MessageValue]] internal slot, then
+                      1. Set _resValue_ to _resValue_.[[MessageValue]].
+                1. Perform ? CreateDataPropertyOrThrow(_options_, _optName_, _resValue_).
+             1. Perform ! CreateDataPropertyOrThrow(_part_, *"options"*, _resOptions_).
+          1. Let _funcArgs_ be « _funcCtx_, _options_ ».
+          1. If _resArg_ is an Object and _resArg_ has a [[MessageValue]] internal slot, then
+             1. Set _resArg_ to _resArg_.[[MessageValue]].
+          1. If _resArg_ is not *undefined*, then
+             1. Append _resArg_ to _funcArgs_.
+          1. Let _funcRes_ be Completion(Call(_function_, *undefined*, _funcArgs_)).
+          1. If _funcRes_ is a normal completion, then
+             1. Let _result_ be OrdinaryObjectCreate(*null*, « [[MessageValue]] »).
+             1. Set _result_.[[MessageValue]] to _funcRes_.[[Value]].
+             1. Return _result_.
+          1. Else,
+             1. Perform ? HandleMessageFormatError(_ctx_, _funcRes_).
+             1. Return ResolveFallback(_source_).
+        </emu-alg>
+      </emu-clause>
+
+      <emu-clause id="sec-resolveunknown" type="abstract operation">
+        <h1>
+          ResolveUnknown (
+            _source_: a String,
+            _value_: an ECMAScript language value
+          ): an Object with an internal slot [[MessageValue]]
+        </h1>
+        <dl class="header">
+          <dt>description</dt>
+          <dd>It resolves an unknown value.</dd>
+        </dl>
+
+        <emu-alg>
+          1. Let _toPartsClosure_ be a new Abstract Closure with no parameters that captures _source_ and _value_ and performs the following steps when called:
+             1. Let _part_ be OrdinaryObjectCreate(%Object.prototype%).
+             1. Perform ! CreateDataPropertyOrThrow(_part_, *"type"*, *"unknown"*).
+             1. Perform ! CreateDataPropertyOrThrow(_part_, *"source"*, _source_).
+             1. Perform ! CreateDataPropertyOrThrow(_part_, *"value"*, _value_).
+             1. Return CreateArrayFromList(« _part_ »).
+          1. Let _toParts_ be CreateBuiltinFunction(_toPartsClosure_, *0*, *"toParts"*, « »).
+          1. Let _toStringClosure_ be a new Abstract Closure with no parameters that captures _value_ and performs the following steps when called:
+             1. Return ? ToString(_value_).
+          1. Let _toString_ be CreateBuiltinFunction(_toStringClosure_, *0*, *"toString"*, « »).
+          1. Let _valueOfClosure_ be a new Abstract Closure with no parameters that captures _value_ and performs the following steps when called:
+             1. Return _value_.
+          1. Let _valueOf_ be CreateBuiltinFunction(_valueOfClosure_, *0*, *"valueOf"*, « »).
+          1. Let _mv_ be OrdinaryObjectCreate(%Object.prototype%).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"type"*, *"unknown"*).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"source"*, _source_).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"locale"*, *"und"*).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"toParts"*, _toParts_).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"toString"*, _toString_).
+          1. Perform ! CreateDataPropertyOrThrow(_mv_, *"valueOf"*, _valueOf_).
+          1. Let _unknown_ be OrdinaryObjectCreate(*null*, « [[MessageValue]] »).
+          1. Set _unknown_.[[MessageValue]] to _mv_.
+          1. Return _unknown_.
+        </emu-alg>
+      </emu-clause>
     </emu-clause>
 
-    <emu-clause id="sec-messagevaluesource" type="abstract operation">
+    <emu-clause id="sec-formatmarkuppart" type="abstract operation">
       <h1>
-        MessageValueSource (
-          _mv_: an Object
-        ): a String
+        FormatMarkupPart (
+          _ctx_: a MessageFormatContext Record,
+          _markup_: an Object,
+        ): an Object
       </h1>
       <dl class="header">
         <dt>description</dt>
-        <dd>
-          It gets the source string representation of a MessageValue,
-          which should be always available.
-          On any error, return the Unicode replacement character � instead.
-        </dd>
+        <dd>It resolves the formatted part value of a markup placeholder.</dd>
       </dl>
 
       <emu-alg>
-        1. Let _source_ be Completion(Get(_mv_, *"source"*)).
-        1. If _source_ is a normal completion, then
-           1. Let _str_ be _source_.[[Value]].
-           1. If _str_ is a String, then
-              1. Return _str_.
-        1. Return *"\uFFFD"*.
+        1. Let _kind_ be ? Get(_markup_, *"kind"*).
+        1. Let _name_ be ? Get(_markup_, *"name"*).
+        1. Let _options_ be ? Get(_markup_, *"options"*).
+        1. Let _part_ be OrdinaryObjectCreate(%Object.prototype%).
+        1. Perform ! CreateDataPropertyOrThrow(_part_, *"type"*, *"markup"*).
+        1. Perform ! CreateDataPropertyOrThrow(_part_, *"kind"*, _kind_).
+        1. Perform ! CreateDataPropertyOrThrow(_part_, *"name"*, _name_).
+        1. If _kind_ is not *"close"* and _options_ is not *undefined*, then
+           1. Let _len_ be ? LengthOfArrayLike(_options_).
+           1. If _len_ > 0, then
+              1. Let _opts_ be ? CreateListFromArrayLike(_options_).
+              1. Let _resOptions_ be OrdinaryObjectCreate(%Object.prototype%).
+              1. For each element _opt_ of _opts_,
+                 1. Let _optName_ be ? Get(_opt_, *"name"*).
+                 1. Let _optValue_ be ? Get(_opt_, *"value"*).
+                 1. Let _resValue_ be ResolveValue(_ctx_, _optValue_).
+                 1. If _resValue_ is an Object, then
+                    1. If _resValue_ has a [[MessageFallback]] internal slot, then
+                       1. Set _resValue_ to *undefined*.
+                    1. Else,
+                       1. Let _valueOf_ be ? Get(_resValue_, *"valueOf"*).
+                       1. If IsCallable(_valueOf_) is *true*, then
+                          1. Let _valueOfResult_ be Completion(Call(_valueOf_, _resValue_)).
+                          1. If _valueOfResult_ is a normal completion, then
+                             1. Set _resValue_ to _valueOfResult_.[[Value]].
+                          1. Else,
+                             1. Perform ? HandleMessageFormatError(_ctx_, _valueOfResult_).
+                             1. Set _resValue_ to *undefined*.
+                 1. Perform ! CreateDataPropertyOrThrow(_resOptions_, _optName_, _resValue_).
+              1. Perform ! CreateDataPropertyOrThrow(_part_, *"options"*, _resOptions_).
+        1. Return CreateArrayFromList(« _part_ »).
       </emu-alg>
     </emu-clause>
 
-    <emu-clause id="sec-resolveexpression" type="abstract operation">
+    <emu-clause id="sec-getsource" type="abstract operation">
       <h1>
-        ResolveExpression (
-          _mf_: an Object,
-          _values_: an Object or undefined,
-          _onError_: a Function or undefined,
-          _expression_: an Object,
-        ): an Object
+        GetSource (
+          _ctx_: a MessageFormatContext Record,
+          _value_: an Object
+        ): a String
       </h1>
       <dl class="header">
         <dt>description</dt>
-        <dd>It resolves the value of an expression for selection and formatting.</dd>
+        <dd>Determines the "source" value for a data model Object.</dd>
       </dl>
 
       <emu-alg>
-        1. ...TODO
+        1. Let _type_ be ? Get(_value_, *"type"*).
+        1. If _type_ is *"literal"*, then
+           1. Let _strValue_ be ? Get(_value_, *"value"*).
+           1. Modify _strValue_ such that all *"\"* characters are replaced with *"\\"*.
+           1. Modify _strValue_ such that all *"|"* characters are replaced with *"\|"*.
+           1. Return the string-concatenation of *"|"*, _strValue_, and *"|"*.
+        1. If _type_ is *"variable"*, then
+           1. Let _name_ be ? Get(_value_, *"name"*).
+           1. Let _local_ be ! Get(_ctx_.[[LocalVariables]], _name_).
+           1. If _local_ has an [[UnresolvedDeclaration]] internal slot, then
+              1. Let _decl_ be _local_.[[UnresolvedDeclaration]].
+              1. If ? Get(_decl_, *"type"*) is *"local"*, then
+                 1. Let _declValue_ be ? Get(_decl_, *"value"*).
+                 1. Return ? GetSource(_ctx_, _declValue_).
+           1. Else if _local_ has a [[MessageValue]] internal slot, then
+              1. Return MessageValueSource(_local_.[[MessageValue]]).
+           1. Else,
+              1. Assert: _local_ has a [[ResolvedName]] internal slot.
+              1. Assert: _local_ has a [[ResolvedValue]] internal slot.
+              1. Set _name_ to _local_.[[ResolvedName]].
+           1. Return the string-concatenation of *"$"* and _name_.
+        1. If _type_ is *"markup"*, then
+           1. Let _kind_ be ? Get(_value_, *"kind"*).
+           1. Let _name_ be ? Get(_value_, *"name"*).
+           1. If _kind_ is *"open"*, return the string-concatenation of *"#"* and _name_.
+           1. If _kind_ is *"standalone"*, return the string-concatenation of *"#"*, _name_, and *"/"*.
+           1. If _kind_ is *"close"*, return the string-concatenation of *"/"* and _name_.
+        1. If _type_ is *"function"*, then
+           1. Let _name_ be ? Get(_value_, *"name"*).
+           1. Return the string-concatenation of *":"* and _name_.
+        1. If _type_ is *"unsupported-annotation"*, then
+           1. Return ? Get(_value_, *"sigil"*).
+        1. If _type_ is *"expression"*, then
+           1. Let _arg_ be ? Get(_value_, *"arg"*).
+           1. If _arg_ is not *undefined*, return ? GetSource(_ctx_, _arg_).
+           1. Let _annotation_ be ? Get(_value_, *"annotation"*).
+           1. If _annotation_ is not *undefined*, return ? GetSource(_ctx_, _annotation_).
+        1. Return *"\uFFFD"*.
       </emu-alg>
+
+      <emu-clause id="sec-messagevaluesource" type="abstract operation">
+        <h1>
+          MessageValueSource (
+            _mv_: an Object
+          ): a String
+        </h1>
+        <dl class="header">
+          <dt>description</dt>
+          <dd>
+            It gets the source string representation of a resolved message value,
+            which should be always available.
+            On any error, return the Unicode replacement character � instead.
+          </dd>
+        </dl>
+
+        <emu-alg>
+          1. Let _source_ be Completion(Get(_mv_, *"source"*)).
+          1. If _source_ is a normal completion, then
+             1. Let _str_ be _source_.[[Value]].
+             1. If _str_ is a String, then
+                1. Return _str_.
+          1. Return *"\uFFFD"*.
+        </emu-alg>
+      </emu-clause>
     </emu-clause>
 
-    <emu-clause id="sec-resolvemessage" type="abstract operation">
+    <emu-clause id="sec-handlemessageformaterror" type="abstract operation">
       <h1>
-        ResolveMessage (
-          _mf_: an Object,
-          _values_: an Object or undefined,
-          _onError_: a Function or undefined,
-        ): a List of Objects
+        HandleMessageFormatError(
+          _ctx_: a MessageFormatContext Record,
+          _completionRecord_: a Completion Record,
+        )
       </h1>
       <dl class="header">
         <dt>description</dt>
-        <dd>It resolves a message during formatting into a List of MessageValue Objects.</dd>
+        <dd>It handles errors during formatting.</dd>
       </dl>
 
       <emu-alg>
-        1. Let _result_ be an empty List.
-        1. Let _pattern_ be ? SelectPattern(_mf_, _values_, _onError_).
-        1. For each element _el_ of _pattern_,
-           1. If _el_ is a String, then
-              1. Append _el_ to _result_.
-           1. Else,
-              1. Let _mv_ be ResolveExpression(_mf_, _values_, _onError_, _el_).
-              1. Append _mv_ to _result_.
-        1. Return _result_.
+        1. Assert: _completionRecord_ is a Completion Record.
+        1. Assert: _completionRecord_ is an abrupt completion.
+        1. Let _onError_ be _ctx_.[[OnError]].
+        1. Let _error_ be _completionRecord_.[[Value]].
+        1. If _onError_ is not *undefined*, then
+           1. Perform ? Call(_onError_, *undefined*, &laquo; _error_ &raquo;).
+        1. Else if an appropriate notification mechanism exists, then
+           1. Issue a warning for _error_.
       </emu-alg>
     </emu-clause>
 
-    <emu-clause id="sec-selectpattern" type="abstract operation">
+    <emu-clause id="sec-resolvefallback" type="abstract operation">
       <h1>
-        SelectPattern (
-          _mf_: an Object,
-          _values_: an Object or undefined,
-          _onError_: a Function or undefined,
-        ): a List of Strings and Objects
+        ResolveFallback (
+          _source_: a String
+        ): an Object with internal slots [[MessageFallback]] and [[MessageValue]]
       </h1>
       <dl class="header">
         <dt>description</dt>
-        <dd>It selects the pattern to format from the message data model.</dd>
+        <dd>It resolves a fallback value.</dd>
       </dl>
 
       <emu-alg>
-        1. Let _msgData_ be _mf_.[[MessageData]].
-        1. Let _msgType_ be ? Get(_msgData_, *"type"*).
-        1. Assert: _msgType_ is a String.
-        1. If _msgType_ is *"message"*, then
-           1. Let _pattern_ be ? Get(_msgData_, *"pattern"*).
-        1. Else,
-           1. Let _selectorsData_ be ? Get(_msgData_, *"selectors"*).
-           1. Let _selectorExpressions_ be ? CreateListFromArrayLike(_selectorsData_, &laquo; Object &raquo;).
-           1. Let _selectors_ be an empty List of Object and Null values.
-           1. For each element _selExp_ of _selectorExpressions_,
-              1. Let _sel_ be ResolveExpression(_mf_, _values_, _onError_, _selExp_).
-              1. Let _selectKeys_ be ? Get(_sel_, *"selectKeys"*).
-              1. If IsCallable(_selectKeys_) is *true*, then
-                 1. Append _sel_ to _selectors_.
-              1. Else,
-                 1. Let _errorCompletion_ be ThrowCompletion(*TypeError*).
-                 1. Perform ? HandleMessageFormatError(_onError_, _errorCompletion_).
-                 1. Append *null* to _selectors_.
-           1. Let _variantsArray_ be ? Get(_msgData_, *"variants"*).
-           1. Let _variants_ be ? CreateListFromArrayLike(_variantsArray_, &laquo; Object &raquo;).
-           1. Let _selectedVariant_ be ? SelectVariant(_selectors_, _variants_, _onError_).
-        1. Let _patternBody_ be ? Get(_pattern_, *"body"*).
-        1. Return ? CreateListFromArrayLike(_patternBody_, &laquo; String, Object &raquo;).
+        1. Let _toPartsClosure_ be a new Abstract Closure with no parameters that captures _source_ and performs the following steps when called:
+           1. Let _part_ be MessageFallbackPart(_source_).
+           1. Return CreateArrayFromList(« _part_ »).
+        1. Let _toParts_ be CreateBuiltinFunction(_toPartsClosure_, *0*, *"toParts"*, « »).
+        1. Let _toStringClosure_ be a new Abstract Closure with no parameters that captures _source_ and performs the following steps when called:
+           1. Return MessageFallbackString(_source_).
+        1. Let _toString_ be CreateBuiltinFunction(_toStringClosure_, *0*, *"toString"*, « »).
+        1. Let _mv_ be OrdinaryObjectCreate(%Object.prototype%).
+        1. Perform ! CreateDataPropertyOrThrow(_mv_, *"source"*, _source_).
+        1. Perform ! CreateDataPropertyOrThrow(_mv_, *"toParts"*, _toParts_).
+        1. Perform ! CreateDataPropertyOrThrow(_mv_, *"toString"*, _toString_).
+        1. Let _fallback_ be OrdinaryObjectCreate(*null*, « [[MessageFallback]], [[MessageValue]] »).
+        1. Set _fallback_.[[MessageValue]] to _mv_.
+        1. Return _fallback_.
       </emu-alg>
+
+      <emu-clause id="sec-messagefallbackpart" type="abstract operation">
+        <h1>
+          MessageFallbackPart (
+            _source_: a String
+          ): an Object
+        </h1>
+        <dl class="header">
+          <dt>description</dt>
+          <dd>It gets the fallback formatted part representation.</dd>
+        </dl>
+
+        <emu-alg>
+          1. Let _result_ be OrdinaryObjectCreate(%Object.prototype%).
+          1. Perform ! CreateDataPropertyOrThrow(_result_, *"type"*, *"fallback"*).
+          1. Perform ! CreateDataPropertyOrThrow(_result_, *"source"*, _source_).
+          1. Return _result_.
+        </emu-alg>
+      </emu-clause>
+
+      <emu-clause id="sec-messagefallbackstring" type="abstract operation">
+        <h1>
+          MessageFallbackString (
+            _source_: a String
+          ): a String
+        </h1>
+        <dl class="header">
+          <dt>description</dt>
+          <dd>It gets the fallback formatted string representation.</dd>
+        </dl>
+
+        <emu-alg>
+          1. Return the string-concatenation of *"{"*, _source_, and *"}"*.
+        </emu-alg>
+      </emu-clause>
     </emu-clause>
 
-    <emu-clause id="sec-selectvariant" type="implementation-defined abstract operation">
+    <emu-clause id="sec-resolvevalue" type="abstract operation">
       <h1>
-        SelectVariant (
-          _selectors_: a List of Object and Null values,
-          _variants_: a List of Objects,
-          _onError_: a Function or undefined,
-        ): an Object
+        ResolveValue (
+          _ctx_: a MessageFormatContext Record,
+          _value_: an Object,
+        ): an ECMAScript language value
       </h1>
       <dl class="header">
         <dt>description</dt>
         <dd>
-          <p>
-            It applies the variant selection method defined by
-            the "Resolve Preferences", "Filter Variants", and "Sort Variants" steps of the
-            <a href="https://github.com/unicode-org/message-format-wg/blob/main/spec/formatting.md#pattern-selection">Pattern Selection</a>
-            section of the Unicode MessageFormat 2.0 specification.
-          </p>
-
-          <p>
-            For the selection, Null values in _selectors_ indicate selectors for which selection will always fail.
-            If any errors are encountered during the selection,
-            the HandleMessageFormatError abstract operation must be called
-            with _onError_ and an abrupt Completion Record containing an Error.
-          </p>
-
-          <p>
-            The value returned by this operation must be an Object matching the JSON Schema definition of a message pattern:
-            <a href="https://github.com/unicode-org/message-format-wg/blob/main/spec/data-model/message.json#/$defs/pattern">
-              https://github.com/unicode-org/message-format-wg/blob/main/spec/data-model/message.json#/$defs/pattern
-            </a>.
-          </p>
+          It resolves the value of a literal or variable reference.
+          For literals, the returned value is always a String.
+          For variable references, the returned value may be any ECMAScript language value.
+          For unresolved variable references, the returned value is an Object with an internal slot [[MessageFallback]].
         </dd>
       </dl>
+
+      <emu-alg>
+        1. Let _type_ be ? Get(_value_, *"type"*).
+        1. If _type_ is *"literal"*, then
+           1. Return ? Get(_value_, *"value"*).
+        1. Assert: _type_ is *"variable"*.
+        1. Let _name_ be ? Get(_value_, *"name"*).
+        1. Let _localVars_ be _ctx_.[[LocalVariables]].
+        1. Let _var_ be ! Get(_localVars_, _name_).
+        1. If _var_ is *undefined*, then
+           1. Set _var_ to ? Get(_ctx_.[[Values]], _name_).
+           1. If _var_ is *undefined*, then
+              1. Let _error_ be ThrowCompletion(*ReferenceError*).
+              1. Perform ? HandleMessageFormatError(_ctx_, _error_).
+              1. Let _source_ be ? GetSource(_value_).
+              1. Set _var_ to ResolveFallback(_source_).
+              1. Perform ! Set(_localVars_, _name_, _var_).
+           1. Else,
+              1. Let _resolved_ be OrdinaryObjectCreate(*null*, « [[ResolvedName]], [[ResolvedValue]] »).
+              1. Set _resolved_.[[ResolvedName]] to _name_.
+              1. Set _resolved_.[[ResolvedValue]] to _var_.
+              1. Perform ! Set(_localVars_, _name_, _resolved_).
+        1. Else,
+           1. Assert: _var_ is an Object.
+           1. If _var_ has a [[ResolvedValue]] internal slot, then
+              1. Set _var_ to _var_.[[ResolvedValue]].
+           1. Else if _var_ has an [[UnresolvedDeclaration]] internal slot, then
+              1. Let _decl_ be _var_.[[UnresolvedDeclaration]].
+              1. Let _declType_ be ? Get(_decl_, *"type"*).
+              1. If _declType_ is *"input"*, then
+                 1. Let _expression_ be ? Get(_decl_, *"value"*).
+                 1. Perform ! Set(_localVars_, _name_, *undefined*).
+                 1. Set _var_ to ? ResolveExpression(_ctx_, _expression_).
+              1. Else if _declType_ is *"local"*, then
+                 1. Let _expression_ be ? Get(_decl_, *"value"*).
+                 1. Set _var_ to ? ResolveExpression(_ctx_, _expression_).
+              1. Else,
+                 1. Let _error_ be ThrowCompletion(*ReferenceError*).
+                 1. Perform ? HandleMessageFormatError(_ctx_, _error_).
+                 1. Let _source_ be ? GetSource(_value_).
+                 1. Set _var_ to ResolveFallback(_source_).
+              1. Perform ! Set(_localVars_, _name_, _var_).
+        1. Return _var_.
+      </emu-alg>
     </emu-clause>
   </emu-clause>
 </emu-clause>