clarify style sheet non-conformance, issues-1#16

Author: fantasai

css3-namespace/Overview.html

@@ -290,9 +290,10 @@ <h3 id=syntax><span class=secno>3.1. </span>Syntax</h3>
 
    <p>A syntactically invalid <code>@namespace</code> rule (whether malformed
     or misplaced) must be <a
-    href="http://www.w3.org/TR/CSS21/conform.html#x22">ignored</a>. A style
-    sheet containing an invalid <code>@namespace</code> rule is
-    non-conforming.</p>
+    href="http://www.w3.org/TR/CSS21/conform.html#x22">ignored</a>. A CSS <a
+    href="http://www.w3.org/TR/CSS21/conform.html#style-sheet">style
+    sheet</a> containing an invalid <code>@namespace</code> rule is itself <a
+    href="http://www.w3.org/TR/CSS21/conform.html#valid-style-sheet">invalid</a>.</p>
 
    <p>A URI string parsed from the <code>URI</code> syntax must be treated as
     a literal string: as with the <code>STRING</code> syntax, no URI-specific

css3-namespace/Overview.src.html

@@ -201,8 +201,9 @@ <h3 id="syntax">Syntax</h3>
 
   <p>A syntactically invalid <code>@namespace</code> rule (whether malformed or
     misplaced) must be <a href="http://www.w3.org/TR/CSS21/conform.html#x22">ignored</a>.
-    A style sheet containing an invalid <code>@namespace</code> rule is
-    non-conforming.</p>
+    A CSS <a href="http://www.w3.org/TR/CSS21/conform.html#style-sheet">style sheet</a>
+    containing an invalid <code>@namespace</code> rule is itself
+    <a href="http://www.w3.org/TR/CSS21/conform.html#valid-style-sheet">invalid</a>.</p>
 
   <p>A URI string parsed from the <code>URI</code> syntax must be treated as
     a literal string: as with the <code>STRING</code> syntax, no URI-specific