[css-typed-om] Fix the type match algo to refer to the percent hint more abstractly.

Author: tabatkins

css-typed-om/Overview.bs

@@ -1896,30 +1896,32 @@ and to the CSS [=math functions=].
     3. Return |result|.
 
 
-A [=type=] is said to match a CSS production in some circumstances:
-
-* A [=type=] matches <>
-    if its only non-zero [=map/entry=] is «[ "length" → 1 ]»
-    and its [=percent hint=] is null.
-    Similarly for <>, <>, <>, <>, and <>.
-* A [=type=] matches <>
-    if its only non-zero [=map/entry=] is «[ "percent" → 1 ]».
-* A [=type=] matches <>
-    if its only non-zero [=map/entry=] is either «[ "length" → 1 ]» or «[ "percent" → 1 ]»
-    Same for <>, <>, etc.
-* A [=type=] matches <>
-    if it has no non-zero [=map/entries=]
-    and its [=percent hint=] is null.
-* A [=type=] matches <>
-    if it has no non-zero [=map/entries=],
-    or its only non-zero [=map/entry=] is «[ "percent" → 1 ]».
-
-Many specifications use ''[ <> | <> ]''
-instead of ''<>'' in their grammar,
-and specify in prose that the <> and <> can be combined.
-For the purposes of [=CSSNumericValue/matching=],
-these cases should be treated as <>.
-Similarly for <>, etc.
+
+    A [=type=] is said to match a CSS production in some circumstances:
+
+    * A [=type=] matches <>
+        if its only non-zero [=map/entry=] is «[ "length" → 1 ]».
+        Similarly for <>, <>, <>, <>, and <>.
+
+        If the context in which the value is used
+        does not allow <> values,
+        then the [=type=] must additionally have
+        a null [=percent hint=]
+        to be considered [=CSSNumericValue/matching=].
+    * A [=type=] matches <>
+        if its only non-zero [=map/entry=] is «[ "percent" → 1 ]».
+    * A [=type=] matches <>
+        if its only non-zero [=map/entry=] is either «[ "length" → 1 ]» or «[ "percent" → 1 ]».
+        Same for <>, <>, etc.
+    * A [=type=] matches <>
+        if it has no non-zero [=map/entries=].
+
+        If the context in which the value is used
+        does not allow <> values,
+        then the [=type=] must additionally have
+        a null [=percent hint=]
+        to be considered [=CSSNumericValue/matching=].
+
 
 Note: [=Types=] form a semi-group under both addition
 and a monoid under multiplication