:scope always refers to the document element, so find(':scope > li') matches nothing #133

Description of the bug

:scope always refers to the document element, never to the element find() was called on. So it can't be used to anchor a search at the current match set, as jQuery's $(el).find(':scope > li') does:

$xml = '<?xml version="1.0"?><root><ul id="u1"><li id="a"/><li id="b"/></ul><ul id="u2"><li id="c"/></ul></root>';

qp($xml, '#u1')->find(':scope > li');              // (none), expected a, b
qp($xml, 'ul')->find(':scope > li');               // (none), expected a, b, c
qp($xml, '#u1')->find('li:not(:scope > li)');      // a, b, expected (none)
qp($xml, '#u1')->find('li:matches(:scope > li)');  // (none), expected a, b
qp($xml)->find(':scope > ul');                     // u1, u2 (correct only because the scope is the root)

Cause

DOMQuery::find() / findInPlace() and DOM's constructor build new DOMTraverser($this->matches) without a scope node, so DOMTraverser falls back to $this->dom->documentElement. The nested traversers for :not() / :matches() (PseudoClass::is()) also pass null, so :scope inside them is the document element even when the outer query had a real scope. Noted in #128.

With more than one element in the set, :scope should match each of them (jQuery runs .find() per element).

QueryPath version

main at 9d04ccf.