code: function cssParseUri(candidate) {
        var string1 = /^\s*["]([^"]*)["]\s*$/;
        var string2 = /^\s*[']([^']*)[']\s*$/;
        var url1 = /^\s*url\s*[(]["]([^"]*)["][)]\s*$/;
        var url2 = /^\s*url\s*[(][']([^']*)['][)]\s*$/;
        // Not officially part of the CSS2.1 grammar
        // but supported by Chrome
        var url3 = /^\s*url\s*[(]([^)]*)[)]\s*$/;
        var match;
        if ((match = string1.exec(candidate))) {
          return match[1];
        } else if ((match = string2.exec(candidate))) {
          return match[1];
        } else if ((match = url1.exec(candidate))) {
          return match[1];
        } else if ((match = url2.exec(candidate))) {
          return match[1];
        } else if ((match = url3.exec(candidate))) {
          return match[1];
        }
        return null;
      }
docs: Extracts a url out of an at-import rule of the form:
  \@import "mystyle.css";
  \@import url("mystyle.css");
  
  Returns null if no valid url was found.