[css-lists-3] Add back paragraph on scoping from CSS2, and tie concepts together using it, so that “innermost” is well-defined and also understandable.

Author: fantasai

css-lists-3/Overview.bs

@@ -820,7 +820,7 @@ Manipulating Counter Values: the 'counter-increment' and 'counter-set' propertie
 	but only the last set value will take effect.
 
 <h3 id='nested-counters'>
-Nested Counters</h3>
+Nested Counters and Scope</h3>
 
 	Counters are “self-nesting”;
 	[=instantiating=] a new counter on an element
@@ -834,6 +834,16 @@ Nested Counters</h3>
 	The ''counter()'' function only retrieves the innermost counter of a given name on the element,
 	whereas the ''counters()'' function uses all counters of a given name that contain the element.
 
+	The <dfn lt="counter scope" local-lt="scope">scope</dfn> of a [=counter=] therefore
+	starts at the first element in the document that [=instantiates=] that counter
+	and includes the element’s descendants and its following siblings with their descendants.
+	However, it does not include any elements in the scope of a counter with the same name
+	created by a 'counter-reset' on a later sibling of the element,
+	allowing such explicit counter instantiations
+	to obscure those earlier siblings.
+
+	See [[#creating-counters]] for the exact rules governing the scope of counters and their values.
+
 	<div class="example" id='counter-nesting-example'>
 		The following code numbers nested list items.
 		The result is very similar to that of setting ''display:list-item'' and ''list-style: inside'' on the LI element:
@@ -895,15 +905,17 @@ Nested Counters</h3>
 Creating and Inheriting Counters</h3>
 
 	Each element or pseudo-element in a document has
-	a (possibly empty) set of [=counters=] associated to the element,
+	a (possibly empty) set of [=counters=] in the [=scope=] of that element,
 	either through inheritance from another element
 	or through instantiation on the element directly.
 	These counters are represented as a <dfn>CSS counters set</dfn>,
 	which is a [=/set=]
 	whose values are [=tuples=] of:
 	a [=string=] (representing a counter’s name),
 	an element (representing the counter’s originating element),
-	and an integer (representing the counter’s value).
+	and an integer (representing the counter’s value),
+	the latest one of a given name
+	representing the “innermost” counter of that name.
 
 	<div algorithm>
 		An element [=inherit counters|inherits=] its initial set of counters