[BUGFIX] Allow comma in selectors (#1293)

Also add a note that the specificity is incorrectly calculated in such cases.
This will be addressed with a separate fix.

Author: JakeQZ

CHANGELOG.md

@@ -55,6 +55,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 ### Fixed
 
+- Allow comma in selectors (e.g. `:not(html, body)`) (#1293)
 - Set line number when `RuleSet::addRule()` called with only column number set
   (#1265)
 - Ensure first rule added with `RuleSet::addRule()` has valid position (#1262)

src/Property/Selector.php

@@ -59,9 +59,9 @@ class Selector
     const SELECTOR_VALIDATION_RX = '/
         ^(
             (?:
-                [a-zA-Z0-9\x{00A0}-\x{FFFF}_^$|*="\'~\[\]()\-\s\.:#+>]* # any sequence of valid unescaped characters
-                (?:\\\\.)?                                              # a single escaped character
-                (?:([\'"]).*?(?<!\\\\)\2)?                              # a quoted text like [id="example"]
+                [a-zA-Z0-9\\x{00A0}-\\x{FFFF}_^$|*="\'~\\[\\]()\\-\\s\\.:#+>,]* # any sequence of valid unescaped characters
+                (?:\\\\.)?                                                      # a single escaped character
+                (?:([\'"]).*?(?<!\\\\)\\2)?                                     # a quoted text like [id="example"]
             )*
         )$
         /ux';