expand type getter steps to ensure "submit" is only returned for vali…

…d submit buttons

source

@@ -53750,9 +53750,31 @@ interface <dfn interface>HTMLButtonElement</dfn> : <span>HTMLElement</span> {
   <p>The <dfn attribute for="HTMLButtonElement"><code data-x="dom-button-value">value</code></dfn>
   IDL attribute must <span>reflect</span> the content attribute of the same name.</p>
 
-  <p>The <dfn attribute for="HTMLButtonElement"><code data-x="dom-button-type">type</code></dfn> IDL
-  attribute must <span>reflect</span> the content attribute of the same name, <span>limited to only
-  known values</span>.</p>
+  <p>The <dfn attribute for="HTMLButtonElement"><code data-x="dom-button-type">type</code></dfn>
+  getter steps are:</p>
+
+
+  <p>The <dfn attribute for="HTMLButtonElement"><code data-x="dom-button-type">type</code></dfn>
+  getter steps are:</p>
+
+  <ol>
+   <li><p>Let <var>type</var> be <span>this</span>'s <span
+   data-x="attr-button-type">type</span> attribute.</p><li>
+
+   <li><p>If <var>type</var> is in the <span
+   data-x="attr-button-type-submit-state">Submit</span> state, and <span>this</span> is a <span
+   data-x="concept-submit-button">submit button</span>, return the string
+   "<code data-x="">submit</code>".</p></li>
+
+   <li><p>If <var>type</var> is in the <span
+   data-x="attr-button-type-reset-state">Reset</span> state, return the string
+   "<code data-x="">reset</code>".</p></li>
+
+   <li><p>Return the string "<code data-x="">button</code>".</p></li>
+  </ol>
+
+  <p>The <code data-x="dom-button-type">type</code> setter steps are to set the <code
+  data-x="attr-button-type">type</code> content attribute to the given value.</p>
 
   <p>The <code data-x="dom-cva-willValidate">willValidate</code>, <code
   data-x="dom-cva-validity">validity</code>, and <code