[css-pseudo] remove alt (moved to css-content)

Author: astearns

css-pseudo/Overview.bs

@@ -578,56 +578,6 @@ Generated Content Pseudo-elements: ''::before'' and ''::after''</h2>
   (<code>:before</code> and <code>:after</code>)
   for these pseudo-elements.
 
-<h3 id="alt-property">
-Alternative text for Generated Content: The 'alt' property</h3>
-
-  The generated content of a ::before or ::after element is not always appropriate for assistive technology. In these cases, alternative text can be provided using the 'alt' property. The 'alt' property applies only to the same elements the 'content' property applies to.
-
-  <pre class=propdef>
-  Name: alt
-  Value: none | <<string>>
-  Initial: none
-  Applies to: ::before and ::after pseudo-elements
-  Inherited: no
-  Computed Value: as specified
-  </pre>
-
-  <dl>
-    <dt>none</dt>
-    <dd>No alternative text</dd>
-
-    <dt><<string>></dt>
-    <dd>The alternative text is the <<string>>. This can be the empty string.</dd>
-  </dl>
-
-  When the alt property computes to anything other than none, the alternative <<string>> should be used instead of the value of the contents property by assistive technology.
-
-  <div class="example">
-
-  Here the content property is an image, so the alt property is required to provide alternative text.
-
-  <pre>
-  .new::before { 
-    content: url(./img/star.png);
-    alt: "New!"; 
-  }
-  </pre>
-  </div>
-
-  <div class="example">
-
-  If the pseudo-element is purely decorative and its function is covered elsewhere, setting alt to the empty string can avoid reading out the decorative element. Here the ARIA attribute will be spoken as "collapsed". Without the empty string alt value, the content would also be spoken as "Black right-pointing pointer".
-
-  <pre>
-  .expandable::before {
-    content: "\25BA"; /* a.k.a. ► */
-    alt: ""; 
-    /* aria-expanded="false" already in DOM, 
-       so this pseudo-element is decorative */
-  }
-  </pre>
-  </div>
-
 <h2 id="interactions">Overlapping Pseudo-element Interactions</h2>
 
   <div class="example" id="overlapping-example">