Shadow: define attachShadow() for custom elements

dom.bs

@@ -6107,9 +6107,11 @@ method, when invoked, must run these steps:
 invoked, must run these steps:
 
 <ol>
- <li><p>If <a>context object</a> is not a <span class=XXX>custom element</span>, and is not an
- <a for=/>element</a> whose <a for=Element>namespace</a> is the <a>HTML namespace</a> and
- <a for=Element>local name</a> is
+ <li><p>If <a>context object</a>'s <a for=Element>namespace</a> is <em>not</em> the
+ <a>HTML namespace</a>, then throw a {{NotSupportedError}} exception.
+
+ <li><p>If <a>context object</a>'s <a for=Element>local name</a> is <em>not</em> a
+ <a>valid custom element name</a>,
  "<code>article</code>",
  "<code>aside</code>",
  "<code>blockquote</code>",

dom.html

@@ -71,7 +71,7 @@
    <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>
    <hgroup>
     <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="2016-04-15">15 April 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="2016-04-16">16 April 2016</time></span></h2>
    </hgroup>
    <div data-fill-with="spec-metadata">
     <dl>
@@ -3483,7 +3483,9 @@ <h3 class="heading settled" data-level="4.9" id="interface-element"><span class=
 invoked, must run these steps: </p>
    <ol>
     <li>
-     <p>If <a data-link-type="dfn" href="#context-object">context object</a> is not a <span class="XXX">custom element</span>, and is not an <a data-link-type="dfn" href="#concept-element">element</a> whose <a data-link-type="dfn" href="#concept-element-namespace">namespace</a> is the <a data-link-type="dfn" href="#html-namespace">HTML namespace</a> and <a data-link-type="dfn" href="#concept-element-local-name">local name</a> is
+     <p>If <a data-link-type="dfn" href="#context-object">context object</a>’s <a data-link-type="dfn" href="#concept-element-namespace">namespace</a> is <em>not</em> the <a data-link-type="dfn" href="#html-namespace">HTML namespace</a>, then throw a <code class="idl"><a data-link-type="idl" href="https://heycam.github.io/webidl/#notsupportederror">NotSupportedError</a></code> exception. </p>
+    <li>
+     <p>If <a data-link-type="dfn" href="#context-object">context object</a>’s <a data-link-type="dfn" href="#concept-element-local-name">local name</a> is <em>not</em> a <a data-link-type="dfn" href="https://rawgit.com/w3c/webcomponents/15a203c8393aef0df7223ab1d43406aa11a7e71e/spec/custom/index.html#dfn-valid-custom-element-name">valid custom element name</a>,
  "<code>article</code>",
  "<code>aside</code>",
  "<code>blockquote</code>",