Issue 6619 - Qualify CSS selectors in document style sheet correctly

lib/common.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 154 matching lines @@
       whitespace = 0;
 
     // Increment the index by the size of the character. Note that for Unicode
     // composite characters (like emoji) this will be more than one.
     index += character.length;
   }
 
   return selector.length - index + whitespace;
 }
 
+/**
+ * Qualifies a CSS selector with a qualifier, which may be another CSS selector
+ * or an empty string. For example, given the selector "div.bar" and the
+ * qualifier "#foo", this function returns "div#foo.bar".
+ * @param {string} selector The selector to qualify.
+ * @param {string} qualifier The qualifier with which to qualify the selector.
+ * @returns {string} The qualified selector.
+ */
 function qualifySelector(selector, qualifier)
 {
   let qualifiedSelector = "";
 
   for (let sub of splitSelector(selector))
   {
     sub = sub.trim();
 
     qualifiedSelector += ", ";
 
     let index = findTargetSelectorIndex(sub);
     let [, type = "", rest] = /^([a-z][a-z-]*)?(.*)/i.exec(sub.substr(index));
 
     // Note that the first group in the regular expression is optional. If it
     // doesn't match (e.g. "#foo::nth-child(1)"), type will be an empty string.
     qualifiedSelector += sub.substr(0, index) + type + qualifier + rest;
   }
 
   // Remove the initial comma and space.
   return qualifiedSelector.substr(2);
 }
 
 exports.qualifySelector = qualifySelector;