[css-lists-3] Counters aren't <<string>>, so define them as their own type like we did in CSS2. #1929

Author: fantasai

css-lists-3/Overview.bs

@@ -1081,20 +1081,21 @@ Counters in elements that do not generate boxes</h3>
 Outputting Counters: the ''counter()'' and ''counters()'' functions</h3>
 
 	Counters have no visible effect by themselves,
-	but their values can be used with the ''counter()'' and ''counters()'' functions.
-	This happens automatically in ''::marker'' pseudo-elements,
-	but can be used by an author anywhere that accepts a <<string>>.  Their syntax is:
+	but their values can be used
+	with the ''counter()'' and ''counters()'' functions,
+	which represent the counter values as strings or images.
+	Their syntax is:
 
 	<pre>
+		<dfn><<counter>></dfn> = <<counter()>> | <<counters()>>
 		<dfn>counter()</dfn>  =  counter( <<custom-ident>>, [ <<counter-style>> | none ]? )
 		<dfn>counters()</dfn> = counters( <<custom-ident>>, <<string>>, [ <<counter-style>> | none ]? )
 	</pre>
 
 	For both functions, the first argument represents the name of a counter,
 	and if the last argument is omitted it defaults to ''decimal''.
 
-	A ''counter()'' represents a <<string>>,
-	obtained as follows:
+	The used value of ''counter()'' is obtained as follows:
 
 	<ul>
 		<li>
@@ -1127,8 +1128,7 @@ Outputting Counters: the ''counter()'' and ''counters()'' functions</h3>
 		</pre>
 	</div>
 
-	A ''counters()'' represents a <<string>>,
-	obtained as follows:
+	The used value of ''counters()'' is obtained as follows:
 
 	<ul>
 		<li>
@@ -1159,10 +1159,6 @@ Outputting Counters: the ''counter()'' and ''counters()'' functions</h3>
 			The function represents the string thus produced.
 	</ul>
 
-	Issue: Counter representations don't have to be strings,
-	they can be images sometimes instead.
-	What to do?
-
 	<div class='example'>
 		The following example shows a simple use of the ''counters()'' function: