Fix An+B explanation to be correct, and add a reminder note about the…

… element list being 1-indexed. Also fix some Bikeshed warnings. Fixes #2321.

selectors-4/Overview.bs

@@ -24,11 +24,16 @@ At Risk: the column combinator
 At Risk: the '':drop()'' pseudo-class
 At Risk: the '':read-write'' pseudo-class
 Ignored Terms: function token, Document, DocumentFragment, math, h1, shadow tree, query(), quirks mode, button, a, span, object, p, div, q, area, link, label, input, html, em, li, ol, pre, CSS Value Definition Syntax
-Ignored Vars: identifier, extended filtering
+Ignored Vars: identifier, extended filtering, i
 </pre>
 <pre class=link-defaults>
 spec:css-syntax-3; type:dfn; text:identifier
 spec:css-display-3; type:property; text:display
+spec:css-pseudo-4; type:selector;
+	text: ::before
+	text: ::after
+	text: ::first-line
+	text: ::first-letter
 </pre>
 
 <style>
@@ -624,7 +629,7 @@ Structure and Terminology</h3>
 	if the type is important and unspecified,
 	it defaults to meaning a <a>list of complex selectors</a>.
 	(See [[#grouping]] for additional information on <a>selector lists</a>
-	and the various <<*-selector-list>> productions in the <a href="#grammar">grammar</a>
+	and the various &lt;*-selector-list> productions in the <a href="#grammar">grammar</a>
 	for their formal syntax.)
 	A given element is said to <a>match</a> a <a>selector list</a>
 	when it matches any (at least one) of the <a>selectors</a>
@@ -2742,7 +2747,11 @@ Child-indexed Pseudo-classes</h3>
 	The <var>An+B</var> notation and its interpretation
 	are defined in [[css-syntax-3#anb-microsyntax]];
 	it represents any index <var>i</var> = <var>A</var><var>n</var> + <var>B</var>
-	for any positive integer <var>n</var>.
+	for any integer <var>n</var> 0 or greater.
+
+	Note: For these purposes, the list of elements is <b>1-indexed</b>;
+	that is, the first child of an element has index 1, and will be matched by '':nth-child(2n+1)'',
+	because when <code>n=0</code> the expression evaluates to ''1''.
 
 	For example, this selector could address every other row in a table,
 	and could be used to alternate the color of paragraph text in a cycle of four.