QuerySelector returning incorrect results when using a grouped selector

[christiango]

Describe the bug
My team is trying to replace JSDOM with happy-dom and we are hitting some unexpected differences in behavior with regards to query selector. In particular, we have a minimal repro of a query selector that does not match the output of JSDOM or chromium.

To Reproduce
This unit test in QuerySelector.test.ts captures the issue.

	it('Supports grouped selectors', () => {
			const div = document.createElement('div');

			div.innerHTML = `
				<div class>
            		<h1><span>Here is a heading</span></h1>
            		<div class="a">
              			<span>With a child span</span>
            		</div>
          		</div>
			`;

			expect(div.querySelector('.a,h1')).toBe(div.children[0].children[0])
		})

Expected behavior
The behavior here is that the div with class a is being returned, instead of the h1 which is what is returned in jsdom and in the browser.

Screenshots
If applicable, add screenshots to help explain your problem.

Device:
Node 22 on Windows, MacOS, and Linux

Additional context

[christiango]

Interestingly querySelectorAll returns the h1 as the first element. I'm going to debug this myself to see if I can track down a fix.