Add element definition and content categories for custom tags

Fixes #454.

assets/styles/respec-complement.css

@@ -88,3 +88,9 @@ body.dfnEnabled dfn { cursor: pointer; }
   padding-top: 0;
   padding-bottom: 0;
 }
+
+/*
+ * From https://resources.whatwg.org/standard.css
+ */
+.element { background: #EEFFEE; color: black; margin: 0 0 1em -0.15em; padding: 0 1em 0.25em 1em; }
+.element:not(:hover) > dt > :link, .element:not(:hover) > dt > :visited { color: inherit; text-decoration: none; }

spec/custom/index.html

@@ -421,6 +421,32 @@ <h3 id="custom-elements-core-concepts">Core concepts</h3>
 
 <p>After a <a>custom element</a> is <a lt="create an element">created</a>, changing the value of the <code>is</code> <a href="https://dom.spec.whatwg.org/#concept-named-attribute">attribute</a> does not change the element's behavior.</p>
 
+<p><a lt="custom tag">Custom tags</a> have the following element definition:</p>
+
+
+<dl class="element">
+    <dt><a href="https://html.spec.whatwg.org/#concept-element-categories">Categories</a>:</dt>
+    <dd><a href="https://html.spec.whatwg.org/#flow-content-2">Flow content</a>.</dd>
+    <dd><a href="https://html.spec.whatwg.org/#phrasing-content-2">Phrasing content</a>.</dd>
+    <dd><a href="https://html.spec.whatwg.org/#palpable-content-2">Palpable content</a>.</dd>
+
+    <dt><a href="https://html.spec.whatwg.org/#concept-element-contexts">Contexts in which custom elements can be used</a>:</dt>
+    <dd>Where <a href="https://html.spec.whatwg.org/#phrasing-content-2">phrasing content</a> is expected.</dd>
+
+    <dt><a href="https://html.spec.whatwg.org/#concept-element-content-model">Content model</a>:</dt>
+    <dd><a href="https://html.spec.whatwg.org/#transparent">Transparent</a>.</dd>
+
+    <dt><a href="https://html.spec.whatwg.org/#concept-element-tag-omission">Tag omission in text/html</a>:</dt>
+    <dd>Neither tag is omissible.</dd>
+
+    <dt><a href="https://html.spec.whatwg.org/#concept-element-attributes">Content attributes</a>:</dt>
+    <dd><a href="https://html.spec.whatwg.org/#global-attributes">Global attributes</a>
+    <dd>Any attributes relevant to the element's functioning, as defined by the author</dd>
+
+    <dt><a href="https://html.spec.whatwg.org/#concept-element-dom">DOM interface</a>:</dt>
+    <dd>Supplied by the author (inherits from <a href="https://html.spec.whatwg.org/#htmlelement"><code>HTMLElement</code></a>).</dd>
+</dl>
+
 <p>A <a>custom tag</a> does not have any special meaning: it <a href="https://html.spec.whatwg.org/#represents">represents</a> its children. A <a>type extension</a> inherits the semantics of the element that it extends.</p>
 
 <p>A <dfn id="valid-custom-element-name">valid custom element name</dfn> is a sequence of characters <var>name</var> that meets all of the following requirements:</p>
@@ -947,6 +973,22 @@ <h3>HTML+: Parsing XHTML documents</h3>
 
 </section>
 
+<section>
+<h3>HTML+: Content Model Updates</h3>
+
+<p class="monkeypatch">HTML has several sections that need to be updated when introducing a new element, or in this case class of elements. Those are:</p>
+
+<ul class="monkeypatch">
+    <li><a href="https://html.spec.whatwg.org/#content-categories">The categories venn diagram</a>'s interactive list should include custom elements in phrasing and flow content.</li>
+    <li><a href="https://html.spec.whatwg.org/#flow-content-2">Flow content</a> should include custom elements</li>
+    <li><a href="https://html.spec.whatwg.org/#phrasing-content-2">Phrasing content</a> should include custom elements</li>
+    <li><a href="https://html.spec.whatwg.org/#palpable-content-2">Palpable content</a> should include custom elements</li>
+    <li><a href="https://html.spec.whatwg.org/#elements-3">The elements index</a> should include a row at the bottom for custom elements</li>
+    <li><a href="https://html.spec.whatwg.org/#element-content-categories">The element content categories index</a> should include custom elements in the flow content, phrasing content, and palpable content sections.</li>
+</ul>
+
+</section>
+
 <section id="element-modifications-to-dom">
 <h3>DOM+: Elements</h3>