W3C main is different. https://www.w3.org/Bugs/Public/show_bug.cgi?id=21908

zcorpan · zcorpan · commit a09aabcc1de7 · 2013-05-03T11:29:52.000+02:00
diff --git a/Overview.src.html b/Overview.src.html
@@ -7,6 +7,7 @@
       @media screen { code { color: #D93B00; } code :link, code :visited { color: inherit; } }
       pre, code { font-size: inherit; font-family: monospace; font-variant: normal; }
       pre strong { color: black; font: inherit; font-weight: bold; background: yellow; }
+      .XXX { color: #E50000; background: white; border: solid red; padding: 0.5em; margin: 1em 0; }
     </style>
     <link class=not-whatwg rel="stylesheet" href="http://www.w3.org/StyleSheets/TR/W3C-[STATUS]">
     <link class=not-w3c rel="stylesheet" href="http://www.whatwg.org/style/specification">
@@ -434,7 +435,7 @@ <h3 id="new-elements">New Elements</h3>
 
       <li><p><code data-anolis-spec=html>main</code>
       can be used as a container for the dominant contents of another element, such as
-      the main content of the page.</p></li>
+      the main content of the page. In W3C HTML5 and W3C HTML 5.1, only one such element is allowed in a document.</p></li>
 
       <li><p><code data-anolis-spec=html>aside</code>
       represents a piece of content that is only slightly related to the
