Make the 'match a grammar' algo a little more precise/correct.

Author: tabatkins

css-typed-om/Overview.bs

@@ -605,7 +605,7 @@ probably in an appendix.
         Return |value|'s associated value.
 
     : If |value| is a {{CSSStyleValue}} subclass,
-    :: If |value| does not [=match a CSS production|match the grammar=] of a [=list-valued property iteration=] of |property|,
+    :: If |value| does not [=match a grammar|match the grammar=] of a [=list-valued property iteration=] of |property|,
         [=throw=] a {{TypeError}}.
 
         If any component of |property|’s CSS grammar has a limited numeric range,
@@ -623,15 +623,34 @@ probably in an appendix.
 </div>
 
 <div algorithm>
-    A {{CSSStyleValue}} is said to <dfn>match a CSS production</dfn>
+    CSS properties express their valid inputs with grammars,
+    which are written with the assumption of being matched against strings parsed into CSS tokens,
+    as defined in [[css-syntax-3/#tokenization]].
+    {{CSSStyleValue}} objects can also be matched against these grammars, however.
+
+    A {{CSSStyleValue}} is said to <dfn for=CSSStyleValue>match a grammar</dfn>
     based on the following rules:
 
-    * A {{CSSKeywordValue}} always matches <<ident>>.
-    * A {{CSSTransformValue}} always matches <<transform-list>>.
-    * A {{CSSPositionValue}} always matches <<position>>.
+    * A {{CSSKeywordValue}} matches an [=ident=] specified in a grammar
+        if its {{CSSKeywordValue/value}} internal slot
+        matches the [=ident=].
+
+        If case-folding rules are in effect normally for that [=ident=]
+        (such as ''Auto'' matching the keyword ''auto'' specified in the grammar for 'width'),
+        they apply to this comparison as well.
+    * A {{CSSTransformValue}} matches <<transform-list>>.
+    * A {{CSSPositionValue}} matches <<position>>.
     * A {{CSSNumericValue}} matches what its type [=CSSNumericValue/matches=].
-    * A {{CSSURLImageValue}} always matches <<url>>.
-    * Any subclass of {{CSSImageValue}} always matches <<image>>.
+    * A {{CSSURLImageValue}} matches <<url>>.
+    * Any subclass of {{CSSImageValue}} matches <<image>>.
+    * A {{CSSUnparsedValue}} matches any grammar.
+    * A direct {{CSSStyleValue}} object (not a subclass)
+        with a non-null {{CSSStyleValue/[[associatedProperty]]}} slot
+        matches the grammar of the property specified in its {{CSSStyleValue/[[associatedProperty]]}} slot,
+        regardless of what it is.
+
+    Note: As the ability to create more complex values in Typed OM increases,
+    this section will become more complex.
 </div>
 
 A [=string=] is a <dfn>custom property name string</dfn>