Various fixes to the parser functions

Some functionality, some code quality.

Fixes #189. Fixes #199. Closes #190. Closes #112.

Author: asamuzaK

lib/constants.js

@@ -4,3 +4,13 @@ module.exports.POSITION_AT_SHORTHAND = {
   first: 0,
   second: 1,
 };
+
+// CSS global values
+// see https://drafts.csswg.org/css-cascade-5/#defaulting-keywords
+module.exports.GLOBAL_VALUES = Object.freeze([
+  'initial',
+  'inherit',
+  'unset',
+  'revert',
+  'revert-layer',
+]);