Fix #991: Define case-sensitivity of the argument to attr()

source

@@ -3594,6 +3594,8 @@ a.setAttribute('href', 'http://example.com/'); // change the content attribute d
      <li>The <dfn data-noexport="" data-x-href="https://drafts.csswg.org/css-values/#vw">'vw'</dfn> unit</li>
      <li>The <dfn data-noexport="" data-x-href="https://drafts.csswg.org/css-values/#in">'in'</dfn> unit</li>
      <li>The <dfn data-noexport="" data-x-href="https://drafts.csswg.org/css-values/#px">'px'</dfn> unit</li>
+     <li>The <dfn data-noexport="" data-x-href="https://drafts.csswg.org/css-values/#funcdef-attr">'attr()'</dfn> function</li>
+     <li>The <dfn data-noexport="" data-x-href="https://drafts.csswg.org/css-values/#funcdef-calc">'calc()'</dfn> function</li>
     </ul>
 
     <p>The term <dfn data-x="css-styling-attribute" data-noexport=""
@@ -24918,7 +24920,8 @@ interface <dfn>HTMLImageElement</dfn> : <span>HTMLElement</span> {
   <span>viewport</span>.
   Other units must be interpreted the same as in Media Queries. <ref spec=MQ></p>
 
-  <p>A <span>source size</span> must not use CSS functions other than the <code data-x="">calc()</code> function.</p>
+  <p>A <span>source size</span> must not use CSS functions other than the <span>'calc()'</span>
+  function.</p>
 
   <p>When asked to <dfn>select an image source</dfn> for a given <code>img</code> element <var>el</var>,
   user agents must do the following:</p>
@@ -25342,7 +25345,7 @@ interface <dfn>HTMLImageElement</dfn> : <span>HTMLElement</span> {
    is a valid non-negative <span>&lt;source-size-value></span>,
    let <var>size</var> be its value
    and remove the <span>component value</span> from <var>unparsed size</var>.
-   Any CSS function other than the <code data-x="">calc()</code> function is invalid.
+   Any CSS function other than the <span>'calc()'</span> function is invalid.
    Otherwise, there is a <span data-x="concept-microsyntax-parse-error">parse error</span>;
    continue to the next iteration of this algorithm.</p></li>
 
@@ -66999,9 +67002,25 @@ contradict people?
 
 <!--ADD-TOPIC:CSS-->
 
-  <h3 id="selectors">Matching HTML elements using selectors</h3>
+  <h3 id="selectors">Matching HTML elements using selectors and CSS</h3>
 
-  <h4>Case-sensitivity</h4>
+  <h4>Case-sensitivity of the CSS <span>'attr()'</span> function</h4>
+
+  <p>The CSS Values and Units specification leaves the case-sensitivity of attribute names for the
+  purpose of the <span>'attr()'</span> function to be defined by the host language. <ref
+  spec=CSSVALUES></p>
+
+  <p>When comparing the attribute name part of a CSS <span>'attr()'</span> function to the names of
+  namespace-less attributes on <span>HTML elements</span> in <span>HTML documents</span>, the name
+  part of the CSS <span>'attr()'</span> function must first be <span>converted to ASCII
+  lowercase</span>. The same function when compared to other attributes must be compared according
+  to its original case. In both cases, the comparison is <span>case-sensitive</span>.</p>
+
+  <p class="note">This is the same as comparing the name part of a CSS <span>attribute
+  selector</span>, specified in the next section.</p>
+
+
+  <h4>Case-sensitivity of selectors</h4>
 
   <p>The Selectors specification leaves the case-sensitivity of element names, attribute names, and
   attribute values to be defined by the host language. <ref spec=SELECTORS></p>