code: public static String trimUrl(final StringBuilder s) {
          final String s1 = trimBy(s, 4, 1).trim();
          if (s1.length() == 0) {
              return s1;
          }
  
          final int end = s1.length() - 1;
          final char c0 = s1.charAt(0);
          if ((c0 == '"' && s1.charAt(end) == '"')
              || (c0 == '\'' && s1.charAt(end) == '\'')) {
              return s1.substring(1, end);
          }
  
          return s1;
      }
docs: Helper that removes the leading "url(", the trailing ")"
  and surrounding quotes from the given string builder.
  @param s the StringBuilder
  @return the trimmed string