[css-text-3] Initial draft proposed clarification to text-transform i…

…nteraction with semantics. #3775

css-text-3/Overview.bs

@@ -423,6 +423,10 @@ Text Processing</h3>
     It has no effect on the underlying content,
     and must not affect the content of a plain text copy &amp; paste operation.
 
+    Note: The 'text-transform' property only affects the presentation layer;
+    correct casing for semantic purposes is expected to be encoded
+    in the source text.
+
     <wpt>
       text-transform/text-transform-copy-paste-001-manual.html
     </wpt>
@@ -558,6 +562,53 @@ Text Processing</h3>
       <pre>abbr:lang(ja) { text-transform: full-width; }</pre>
     </div>
 
+    Note: The purpose of 'text-transform' is
+    to allow for presentational casing transformations
+    without affecting the semantics of the document.
+    Note in particular that 'text-transform' casing operations are lossy,
+    and can distort the meaning of a text.
+    While accessiblity interfaces may wish to convey
+    the apparent casing of the rendered text,
+    the transformed text cannot be relied on accurately represent
+    the underlying meaning of the document.
+
+    <div class="example">
+      In this example,
+      the first line of text is capitalized as a visual effect.
+
+      <pre highlight=css>
+        section > p:first-of-type::first-line {
+          text-transform: uppercase;
+        }
+      </pre>
+
+      This effect cannot be written into the source document
+      because the position of the line break depends on layout.
+      But also, the capitalization is not reflecting a semantic distinction
+      and is not intended to affect the paragraph’s reading;
+      therefore it belongs in the presentation layer.
+    </div>
+
+    <div class="example">
+      In this example,
+      the [=ruby=] annotations,
+      which are half the size of the main paragraph text,
+      are transformed to use regular-size kana
+      in place of [=small kana=].
+
+      <pre highlight=css>
+        rt { font-size: 50%; text-transform: full-size-kana; }
+        :is(h1, h2, h3, h4) rt { text-transform: none; /* unset for large text*/ }
+      </pre>
+
+      Note that while this makes such letters easier to see at small type sizes,
+      the transformation distorts the text:
+      the reader needs to mentally substitute [=small kana=]
+      in the appropriate places--
+      not unlike reading a text in English
+      with all “s” characters substituted by “f”.
+    </div>
+
     <p class="note">
       Note: As defined in <a href="#order">Text Processing Order of Operations</a>,
       transforming text affects line-breaking and other formatting operations.