make select button inert

Author: josepharhar

source

@@ -53727,6 +53727,10 @@ interface <dfn interface>HTMLButtonElement</dfn> : <span>HTMLElement</span> {
   <p>A <dfn data-x="attr-button-command-custom">custom command keyword</dfn> is a string that
   <span>starts with</span> "<code data-x="">--</code>".</p>
 
+  <p>If a <code>button</code> element is the first <span data-x="concept-tree-child">child</span>
+  which is an <span>element</span> of a <code>select</code> element, then it is
+  <span>inert</span>.</p>
+
   <div w-nodev>
 
   <p>A <code>button</code> element <var>element</var>'s <span>activation behavior</span> given