Shadow: fix definition of form.elements

Tests: web-platform-tests/wpt#6891.

Fixes whatwg#2795.

Author: hzr

source

@@ -42770,7 +42770,7 @@ interface <dfn>HTMLFormElement</dfn> : <span>HTMLElement</span> {
 
   <p>The <dfn><code data-x="dom-form-elements">elements</code></dfn> IDL attribute must return an
   <code>HTMLFormControlsCollection</code> rooted at the <code>form</code> element's
-  <span>node document</span>, whose filter matches <span data-x="category-listed">listed elements</span>
+  <span>root</span>, whose filter matches <span data-x="category-listed">listed elements</span>
   whose <span>form owner</span> is the <code>form</code> element, with the exception of <code>input</code>
   elements whose <code data-x="attr-input-type">type</code> attribute is in the <span
   data-x="attr-input-type-image">Image Button</span> state, which must, for historical reasons, be