Nowadays CSS selectors are the standard way to query for some HTML elements, because these selectors are much shorter than XPath expressions, e.g. span#color div.red for ( element-with-id("blue")[name() = "span"]//div[tokenize(@class) = "red"] ). The alternative using contains-token ( element-with-id("blue")[name() = "span"]//div[contains-token(@class, "red")]  ) is even longer.

Thus for HTML a function fn:css($selector as string) that evaluates a CSS selector on the descendants of the context item would be more useful, e.g. css("span#color div.red")