[selectors] Remove the restriction on nesting :not() and :matches() inside of not, as it's easily bypassable by just using a selector list.

Author: tabatkins

selectors/Overview.bs

@@ -1231,17 +1231,14 @@ The Matches-Any Pseudo-class: '':matches()''</h3>
 <h3 id="negation">
 The Negation Pseudo-class: '':not()''</h3>
 
-	The negation pseudo-class, <dfn id='negation-pseudo'>:not()</dfn>, is a
-	functional pseudo-class taking a <a href="#grouping">selector list</a>
-	as an argument. It represents an element that is not represented
-	by its argument.
+	The negation pseudo-class, <dfn id='negation-pseudo'>:not()</dfn>,
+	is a functional pseudo-class taking a <a>selector list</a> as an argument.
+	It represents an element that is not represented by its argument.
 
 	Note: In Selectors Level 3,
 	only a single <a>simple selector</a> was allowed as the argument to '':not()''.
 
-	A negation may not be nested within itself or within '':matches()'':
-	'':not(:not(...))'' and '':matches(:not(...))'' are invalid.
-	Additionally, pseudo-elements cannot be represented by the negation pseudo-class;
+	Pseudo-elements cannot be represented by the negation pseudo-class;
 	they are not valid within '':not()''.
 
 	<div class="example">
@@ -1250,7 +1247,7 @@ The Negation Pseudo-class: '':not()''</h3>
 
 		<pre>button:not([DISABLED]) </pre>
 
-		The following selector represents all but <a element title=''>FOO</a> elements.
+		The following selector represents all but <a element title>FOO</a> elements.
 
 		<pre>*:not(FOO)</pre>
 
@@ -1264,11 +1261,9 @@ The Negation Pseudo-class: '':not()''</h3>
 	within a negation pseudo-class unless the argument is an explicit universal
 	selector or a type selector. (See '':matches()''for examples.)
 
-	Note: The '':not()'' pseudo allows
-	useless selectors to be written.  For instance '':not(*|*)'',
-	which represents no element at all, or ''foo:not(bar)'',
-	which is equivalent to ''foo'' but with a higher
-	specificity.
+	Note: The '':not()'' pseudo-class allows useless selectors to be written.
+	For instance '':not(*|*)'', which represents no element at all,
+	or ''div:not(span)'', which is equivalent to ''div'' but with a higher specificity.
 
 <h3 id='relational'>
 The Relational Pseudo-class: '':has()''</h3>

selectors/Overview.html

@@ -1473,17 +1473,14 @@ <h3 class="heading settled heading" data-level=4.2 id=matches><span class=secno>
 <h3 class="heading settled heading" data-level=4.3 id=negation><span class=secno>4.3 </span><span class=content>
 The Negation Pseudo-class: <a class=css data-link-type=maybe href=#negation-pseudo title=:not()>:not()</a></span><a class=self-link href=#negation></a></h3>
 
-<p>The negation pseudo-class, <dfn class=css-code data-dfn-type=selector data-export="" id=negation-pseudo>:not()<a class=self-link href=#negation-pseudo></a></dfn>, is a
-	functional pseudo-class taking a <a href=#grouping>selector list</a>
-	as an argument. It represents an element that is not represented
-	by its argument.</p>
+<p>The negation pseudo-class, <dfn class=css-code data-dfn-type=selector data-export="" id=negation-pseudo>:not()<a class=self-link href=#negation-pseudo></a></dfn>,
+	is a functional pseudo-class taking a <a data-link-type=dfn href=#selector-list title="selector list">selector list</a> as an argument.
+	It represents an element that is not represented by its argument.</p>
 
 <p class=note>Note: In Selectors Level 3,
 	only a single <a data-link-type=dfn href=#simple title="simple selector">simple selector</a> was allowed as the argument to <a class=css data-link-type=maybe href=#negation-pseudo title=:not()>:not()</a>.</p>
 
-<p>A negation may not be nested within itself or within <a class=css data-link-type=maybe href=#matches-pseudo title=:matches()>:matches()</a>:
-	<span class=css data-link-type=maybe title=:not(:not(...))>:not(:not(...))</span> and <span class=css data-link-type=maybe title=:matches(:not(...))>:matches(:not(...))</span> are invalid.
-	Additionally, pseudo-elements cannot be represented by the negation pseudo-class;
+<p>Pseudo-elements cannot be represented by the negation pseudo-class;
 	they are not valid within <a class=css data-link-type=maybe href=#negation-pseudo title=:not()>:not()</a>.</p>
 
 	<div class=example>
@@ -1506,11 +1503,9 @@ <h3 class="heading settled heading" data-level=4.3 id=negation><span class=secno
 	within a negation pseudo-class unless the argument is an explicit universal
 	selector or a type selector. (See <a class=css data-link-type=maybe href=#matches-pseudo title=:matches()>:matches()</a>for examples.)</p>
 
-<p class=note>Note: The <a class=css data-link-type=maybe href=#negation-pseudo title=:not()>:not()</a> pseudo allows
-	useless selectors to be written.  For instance <span class=css data-link-type=maybe title=:not(*|*)>:not(*|*)</span>,
-	which represents no element at all, or <span class=css data-link-type=maybe title=foo:not(bar)>foo:not(bar)</span>,
-	which is equivalent to <span class=css data-link-type=maybe title=foo>foo</span> but with a higher
-	specificity.</p>
+<p class=note>Note: The <a class=css data-link-type=maybe href=#negation-pseudo title=:not()>:not()</a> pseudo-class allows useless selectors to be written.
+	For instance <span class=css data-link-type=maybe title=:not(*|*)>:not(*|*)</span>, which represents no element at all,
+	or <span class=css data-link-type=maybe title=div:not(span)>div:not(span)</span>, which is equivalent to <span class=css data-link-type=maybe title=div>div</span> but with a higher specificity.</p>
 
 <h3 class="heading settled heading" data-level=4.4 id=relational><span class=secno>4.4 </span><span class=content>
 The Relational Pseudo-class: <a class=css data-link-type=maybe href=#has-pseudo title=:has()>:has()</a></span><a class=self-link href=#relational></a></h3>