[css-values-5] Fix grammar errors in if() notation w3c#10064 w3c#5624 w3c#5009 w3c#6638 w3c#4731 w3c#3455

Author: fantasai

css-values-5/Overview.bs

@@ -1253,9 +1253,10 @@ Conditional Value Selection: the ''if()'' notation</h3>
 	Its argument consists of an ordered semi-colon&ndash;separated list of statements,
 	each consisting of a condition
 	followed by a colon
-	followed by the value represented by this notation
-	if the corresponding condition is the first in the list to be true.
-	If no condition matches,
+	followed by a value.
+	An ''if()'' notation represents
+	the value corresponding to the first condition in its argument list to be true;
+	if no condition matches,
 	then the ''if()'' notation represents an empty token stream.
 
 	Note: [=Arbitrary substitution functions=] all resolve at [=computed value=] time;
@@ -1269,12 +1270,15 @@ Conditional Value Selection: the ''if()'' notation</h3>
 	<dfn><<if()>></dfn> = if( [ <<if-condition>> : <<declaration-value>>? ; ]*
 	             <<if-condition>> : <<declaration-value>>? ;? )
 	<dfn><<if-condition>></dfn> =
-	  supports( [ <supports-condition> | <declaration> ] ) |
+	  supports( [ <<supports-condition>> | <<ident>> : <<declaration-value>> ] ) |
 	  media( <<media-query>> ) |
 	  style( <<style-query>> ) |
 	  else
 	</pre>
 
+	The <dfn value for="if()">else</dfn> keyword represents
+	a condition that is always true.
+
 	ISSUE: Incorporate boolean syntax for combining these queries.
 
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