[css-shadow-parts-1] use colon as separator

Author: fergald

css-shadow-parts-1/Overview.bs

@@ -210,11 +210,11 @@ The exposedparts attribute is parsed as a comma-separated list of part mappings.
 Each part mapping is one of:
 
 <dl class=switch>
-    : <code>innerIdent outerIdent</code>
+    : <code>innerIdent : outerIdent</code>
     :: this adds «[ outerIdent → innerIdent ]» to el's <a>part name map</a>.
 
     : <code>ident</code>
-    :: Is shorthand for <code>ident ident</code>.
+    :: Is shorthand for <code>ident : ident</code>.
 
     : anything else
     :: Ignored for error-recovery / future compat.
@@ -224,11 +224,8 @@ Note: It's okay to map a sub-part to several names.
 
 Issue(w3c/csswg-drafts#2411): Decide whether we use "inner outer" or "outer inner"
 
-Issue(w3c/csswg-drafts#2411): Decide whether we use a separator between inner and outer idents.
-E.g. "inner => outer" or "inner : outer".
-
-Issue(w3c/csswg-drafts#2411): Decide whether to allow "ident1 => ident2 ident3 ..."
-as shorthand for "ident1 ident2, ident1 ident3, ...".
+Issue(w3c/csswg-drafts#2411): Decide whether to allow "ident1 : ident2 ident3 ..."
+as shorthand for "ident1 : ident2, ident1 : ident3, ...".
 
 Issue(w3c/csswg-drafts#2411): Decide whether to allow wild-card forwarding,
 e.g exposedparts="button-* buttons".