private Expression extractUrlParameter(HiddenTokenAwareTree token, String function, String text) {
if (text == null)
return null;
if (text.length() <= function.length() + 2)
return new CssString(token, "", "");
String string = text.substring(function.length() + 1, text.length() - 1);
if (!URIUtils.isQuotedUrl(string))
return new CssString(token, string, "");
String quote = String.valueOf(string.charAt(0));
return new CssString(token, string.substring(1, string.length() - 1), quote);
}