Clarify default attribute requirements http://lists.w3.org/Archives/Public/www-style/2009Nov/0022.html

Author: fantasai

selectors3/Overview.html

@@ -1069,18 +1069,21 @@ <h4><a name=attrnmsp>6.3.3. Attribute selectors and namespaces</a></h4>
 
 <h4><a name=def-values>6.3.4. Default attribute values in DTDs</a></h4>
 
-<p>Attribute selectors represent explicitly set attribute values in
-the document tree. Default attribute values may be defined in a DTD or
-elsewhere, but cannot always be selected by attribute
-selectors. Selectors should be designed so that they work even if the
-default values are not included in the document tree.</p>
-
-<p>More precisely, a UA is <em>not</em> required to read an "external
+<p>Attribute selectors represent attribute values in the document tree.
+How that document tree is constructed is outside the scope of Selectors.
+In some document formats default attribute values can be defined in a DTD or
+elsewhere, but these can only be selected by attribute selectors if they
+appear in the document tree. Selectors should be designed so that they
+work whether or not the default values are included in the document tree.</p>
+
+<p>For example, a XML UA may, but is <em>not</em> required to read an "external
 subset" of the DTD but <em>is</em> required to look for default
 attribute values in the document's "internal subset." (See, e.g., <a
-href="#refsXML10">[XML10]</a> for definitions of these subsets.)</p>
+href="#refsXML10">[XML10]</a> for definitions of these subsets.) Depending
+on the UA, a default attribute value defined in the external subset of the
+DTD might or might not appear in the document tree.</p>
 
-<p>A UA that recognizes an XML namespace is not required to use its
+<p>A UA that recognizes an XML namespace may, but is not required to use its
 knowledge of that namespace to treat default attribute values as if
 they were present in the document. (For example, an XHTML UA is not
 required to use its built-in knowledge of the XHTML DTD. See, e.g., <a
@@ -1104,7 +1107,7 @@ <h4><a name=def-values>6.3.4. Default attribute values in DTDs</a></h4>
 <pre>EXAMPLE[radix=decimal] { /*... default property settings ...*/ }
 EXAMPLE[radix=octal]   { /*... other settings...*/ }</pre>
 
-<p>the first rule will not match elements whose <code>radix</code> attribute is
+<p>the first rule might not match elements whose <code>radix</code> attribute is
 set by default, i.e. not set explicitly. To catch all cases, the
 attribute selector for the default value must be dropped:</p>