code: public static String extractURI(String uri) {
  		String ret = uri.substring(4, uri.length()-1).trim();
  		// trim string
  		if(ret.length() > 0 && (ret.charAt(0)=='\'' || ret.charAt(0)=='"'))
  			ret = ret.substring(1, ret.length()-1);
  
  		return ret;
  	}
docs: Considers text as content of URI token,
  and models view at this text as an common string,
  that is removed {@code 'url('} from the beginning
  and {@code ')'} from the and. If result of this operation
  is STRING, remove even quotation marks
  @param uri Content of URI token
  @return String with trimmed URI syntax sugar and
  optionally quotation marks