SimpleXML xpath should warn when returning other return types than node lists

[nielsdos]

Description

Currently, the xpath method only returns node lists. So for example, functions like count(), boolean(), string(), ... don't work.
Very simple (and silly) example:

<?php

$xml = "<container><foo/><foo/></container>";
$sxe = simplexml_load_string($xml);

var_dump($sxe->xpath("count(//foo)"));
var_dump(count($sxe->xpath("//foo")));

3v4l: https://3v4l.org/nmD4k

I expect the output to be twice int(2), instead the output from xpath is an empty array.
Either we should have an additional method for arbitrary xpath evaluations (like in the case of DOM), or the xpath method should be changed to auto-detect the return type of the query. Both are feasibly, but the last one could be a BC break because of the return type change.

[nielsdos]

Changing the issue a bit to make the goal warning the user that the expression is wrong. Changing the actual return type may be a too big BC break.