Clarify the value comparison in input.value's setter

This is a follow-up to whatwg#2437, which introduced the value comparison and
its impact on selection. See
web-platform-tests/wpt#5147 (comment).

source

@@ -48658,10 +48658,11 @@ You cannot submit this form when the field is incorrect.</samp></pre>
      <li><p>Invoke the <span>value sanitization algorithm</span>, if the element's <code
      data-x="attr-input-type">type</code> attribute's current state defines one.</p></li>
 
-     <li><p>If the new value is different from <var>oldValue</var> and the element has a text entry
-     cursor position, move the text entry cursor position to the end of the text control,
-     unselecting any selected text and <span data-x="set the selection direction">resetting the
-     selection direction</span> to "<code data-x="">none</code>".</p></li>
+     <li><p>If the element's <span data-x="concept-fe-value">value</span> (after applying the
+     <span>value sanitization algorithm</span>) is different from <var>oldValue</var>, and the
+     element has a text entry cursor position, move the text entry cursor position to the end of the
+     text control, unselecting any selected text and <span data-x="set the selection
+     direction">resetting the selection direction</span> to "<code data-x="">none</code>".</p></li>
     </ol>
    </dd>