Use integer over An+B syntax for :heading()

See w3c/csswg-drafts#12599

Author: keithamus

source

@@ -76406,11 +76406,11 @@ Demos:
    <code>h1</code>, <code>h2</code>, <code>h3</code>, <code>h4</code>, <code>h5</code>, and
    <code>h6</code> elements.</p></dd>
 
-   <dt><dfn selector noexport data-x="selector-heading-functional">:heading(<var>An+B</var>#)</dfn></dt>
-   <dd><p>The <code data-x="selector-heading-functional">:heading(<var>An+B</var>#)</code>
+   <dt><dfn selector noexport data-x="selector-heading-functional">:heading(<var>integer</var>#)</dfn></dt>
+   <dd><p>The <code data-x="selector-heading-functional">:heading(<var>integer</var>#)</code>
    pseudo-class must match all <code>h1</code>, <code>h2</code>, <code>h3</code>, <code>h4</code>,
-   <code>h5</code>, and <code>h6</code> elements that have a <span>heading level</span> among
-   <var>An+B</var>. <ref>CSSSYNTAX</ref> <ref>CSSVALUES</ref></p></dd>
+   <code>h5</code>, and <code>h6</code> elements that have a <span>heading level</span> of
+   <var>integer</var>. <ref>CSSSYNTAX</ref> <ref>CSSVALUES</ref></p></dd>
 
    <dt><dfn selector noexport><code data-x="selector-playing">:playing</code></dfn></dt>
    <dd>