[css-text-3] Treat CR as spaces

Closes #5410

Author: frivoal

css-text-3/Overview.bs

@@ -1190,7 +1190,9 @@ Order of Operations</h4>
 
   <p>
     Control characters (<a>Unicode category</a> <code>Cc</code>)--
-    other than tabs (U+0009), line feeds (U+000A),
+    other than tabs (U+0009),
+	line feeds (U+000A),
+	carriage returns (U+000D)
     and sequences that form a <a>segment break</a>--
     must be rendered as a visible glyph
     which the UA must synthethize if the glyphs found in the font are not visible,
@@ -1270,6 +1272,16 @@ Order of Operations</h4>
       white-space/control-chars-09F.html
     </wpt>
 
+    Carriage returns (U+000D) are treated identically to spaces (U+0020) in all respects.
+
+    Note: For HTML documents,
+    carriage returns present in the source code
+    are converted to line feeds at the parsing stage
+    and therefore do no appear as U+000D to CSS.
+    However, the character <em>is</em> preserved--
+    and the above rule observable--
+    when encoded using an escape sequence (<code class=lang-html>&amp;#x0d;</code>).
+
   <h3 id="white-space-rules">
     The White Space Processing Rules</h3>
 

css-text-3/test-coverage.html

@@ -133,6 +133,7 @@ <h2 id="white-space-processing-details">4 <a href="https://drafts.csswg.org/css-
 
 <ul>
 	<li>As required by [UNICODE], unsupported Default_ignorable characters must be ignored for rendering.
+	<li>Carriage returns (U+000D) are treated identically to spaces (U+0020) in all respects.
 </ul>
 
 <h3 id="the-white-space-processing-rules">4.1 <a href="https://drafts.csswg.org/css-text-3/#white-space-rules">The White Space Processing Rules</a></h3>