code: public static boolean isURLValue (@Nullable final String sValue)
    {
      final String sRealValue = StringHelper.trim (sValue);
      if (StringHelper.hasNoText (sRealValue))
        return false;
  
      if (sRealValue.equals (CCSSValue.NONE))
        return true;
  
      // 5 = "url(".length () + ")".length
      return sRealValue.length () > 5 &&
             sRealValue.startsWith (CCSSValue.PREFIX_URL_OPEN) &&
             sRealValue.endsWith (CCSSValue.SUFFIX_URL_CLOSE);
    }
docs: Check if the passed CSS value is an URL value. This is either a URL
  starting with "url(" or it is the string "none".
  
  @param sValue
  The value to be checked.
  @return <code>true</code> if the passed value starts with "url(" and ends
  with ")" - <code>false</code> otherwise.