[3003] Allow mathematical expressions in image sizes

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      <li>The <dfn data-x-href="https://drafts.csswg.org/css-values/#in">'in'</dfn> unit</li>
      <li>The <dfn data-x-href="https://drafts.csswg.org/css-values/#px">'px'</dfn> unit</li>
      <li>The <dfn data-x-href="https://drafts.csswg.org/css-values/#funcdef-attr">'attr()'</dfn> function</li>
-     <li>The <dfn data-x-href="https://drafts.csswg.org/css-values/#funcdef-calc">'calc()'</dfn> function</li>
+     <li>The <dfn data-x-href="https://drafts.csswg.org/css-values/#math-function">math functions</dfn></li>
     </ul>
 
     <p>The term <dfn data-x="css-styling-attribute"
 <dfn>&lt;source-size-value></dfn> = <span>&lt;length></span></pre>
 
   <p>A <span>&lt;source-size-value></span> must not be negative, and must not use CSS functions
-  other than the <span>'calc()'</span> function.</p>
+  other than the <span>math functions</span>.</p>
 
   <p>The <span>&lt;source-size-value></span> gives the intended layout width of the image. The
   author can specify different widths for different environments with
    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 <span>'calc()'</span> function is invalid.
+   Any CSS function other than the <span>math functions</span> 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>