[css-sizing-4] Allow metas appearing between head and body to still affect the responsive sizing flag, since they're reparented into the head.

Author: tabatkins

css-sizing-4/Overview.bs

@@ -35,6 +35,7 @@ spec:css2; type:property
 spec:html; type:element;
 	text:meta
 	text:head
+	text:body
 spec:css2; type:dfn; text:document language
 </pre>
 
@@ -1281,7 +1282,8 @@ HTML <{iframe}> Details</h4>
 
 	* If a <code highlight=html>&lt;meta name=responsive-embedded-sizing></code> element is encountered,
 		it is set to true.
-	* If the <{head}> element is closed (explicitly or implicitly),
+	* If the <{body}> element is opened (explicitly or implicitly),
+		or inserted into the document by the parser,
 		it is set to false.
 
 	Once set to either true or false,
@@ -1291,6 +1293,16 @@ HTML <{iframe}> Details</h4>
 	is the only way for an embedded document to opt into this feature in HTML.
 	This means that SVG documents in <{iframe}> cannot do so.
 
+	Note: Due to quirks of the HTML parser,
+	a <{meta}> element can technically appear <em>between</em> the <{head}> and <{body}> elements,
+	and will be reparented into the <{head}>.
+	This is still a valid location for the <code>&lt;meta name=responsive-embedded-sizing></code> element,
+	as the <{body}> has not yet been opened.
+	Note that most HTML elements will implicitly open a <{body}> element
+	even if the <{body}> start tag is not present,
+	and if the document completely lacks such an element,
+	an empty one is automatically generated and inserted.
+
 	The [=internal layout intrinsic size=] is first set
 	by the results of the embedded document's first layout
 	after it fires its {{DOMContentLoaded}} event,