Editorial: define "in a document" better

dom.bs

@@ -5370,9 +5370,8 @@ The <dfn export>document element</dfn> of a
 <p class="note no-backref">Per the <a>node tree</a> constraints, there can only be one
 such <a for="/">element</a>.
 
-When an <a for="/">element</a> or one of its
-<a>ancestors</a> is the
-<a>document element</a>, it is <dfn export>in a document</dfn>.
+<p>An <a for=/>element</a> is <dfn export>in a document</dfn> if its <a>root</a> is a
+<a>document</a>.
 
 <hr>
 

dom.html

@@ -69,7 +69,7 @@
   <div class="head">
    <p data-fill-with="logo"><a class="logo" href="https://whatwg.org/"> <img alt="WHATWG" height="100" src="https://resources.whatwg.org/logo-dom.svg"> </a> </p>
    <h1 class="p-name no-ref allcaps" id="title">DOM</h1>
-   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Living Standard — Last Updated <time class="dt-updated" datetime="2016-03-17">17 March 2016</time></span></h2>
+   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Living Standard — Last Updated <time class="dt-updated" datetime="2016-03-18">18 March 2016</time></span></h2>
    <div data-fill-with="spec-metadata">
     <dl>
      <dt>Participate:
@@ -2960,7 +2960,7 @@ <h3 class="heading settled" data-level="4.9" id="interface-element"><span class=
    <p>The <dfn data-dfn-type="dfn" data-export="" id="document-element">document element<a class="self-link" href="#document-element"></a></dfn> of a <a data-link-type="dfn" href="#concept-document">document</a> is the <a data-link-type="dfn" href="#concept-element">element</a> whose <a data-link-type="dfn" href="#concept-tree-parent">parent</a> is that <a data-link-type="dfn" href="#concept-document">document</a>, if it exists, and null otherwise.</p>
    <p class="note no-backref" role="note">Per the <a data-link-type="dfn" href="#concept-node-tree">node tree</a> constraints, there can only be one
 such <a data-link-type="dfn" href="#concept-element">element</a>. </p>
-   <p>When an <a data-link-type="dfn" href="#concept-element">element</a> or one of its <a data-link-type="dfn" href="#concept-tree-ancestor">ancestors</a> is the <a data-link-type="dfn" href="#document-element">document element</a>, it is <dfn data-dfn-type="dfn" data-export="" id="in-a-document">in a document<a class="self-link" href="#in-a-document"></a></dfn>.</p>
+   <p>An <a data-link-type="dfn" href="#concept-element">element</a> is <dfn data-dfn-type="dfn" data-export="" id="in-a-document">in a document<a class="self-link" href="#in-a-document"></a></dfn> if its <a data-link-type="dfn" href="#concept-tree-root">root</a> is a <a data-link-type="dfn" href="#concept-document">document</a>. </p>
    <hr>
    <dl class="domintro">
     <dt><var>namespace</var> = <var>element</var> . <code class="idl"><a data-link-type="idl" href="#dom-element-namespaceuri">namespaceURI</a></code>