Parsing of CSS predicates.

This adds support for parsing expressions such as "foo[class]".

lib/oga/css/parser.y

@@ -30,7 +30,8 @@ rule
     ;
 
   node_test
-    : node_name { s(:test, *val[0]) }
+    : node_name           { s(:test, *val[0]) }
+    | node_name predicate { s(:test, *val[0], val[1]) }
     ;
 
   node_name
@@ -43,6 +44,10 @@ rule
     # |foo
     | T_PIPE T_IDENT { [nil, val[1]] }
     ;
+
+  predicate
+    : T_LBRACK expression T_RBRACK { val[1] }
+    ;
 end
 
 ---- inner