[Enesuygurs]

Description

hx-swap="scroll:top scrollTarget:window" and hx-swap="show:top showTarget:window" don't scroll the page. __findExt resolves the window extended selector to the window object, which has no scrollTop and no scrollIntoView. So in the scroll case __handleScroll sets a property that has no effect, and in the show case the scrollIntoView?.() call is silently skipped.

htmx 4 suggests this form as the replacement for the old show:window:top / scroll:window:top syntax, and the upgrade checker rewrites show:window:top to show:top showTarget:window. As a result, upgraded pages lose their scroll-to-top behaviour.

This change maps window to document.scrollingElement for both scrollTarget and showTarget. It also updates the hx-swap reference: its "Scroll the window" example still used the removed scroll:window:top form, which now parses as scroll: "window:top" and does nothing.

<div hx-get="/items" hx-swap="innerHTML scroll:top scrollTarget:window">Load</div>
<div style="height:5000px"></div>

Scroll down and click: before this change the page stays where it is, after it the page scrolls back to the top.

Corresponding issue: related to #3544

Testing

I added two tests to test/tests/attributes/hx-swap.js:

• scroll:top scrollTarget:window scrolls the page back to the top. Without the fix it fails with expected 1016 to equal +0.
• show:bottom showTarget:window scrolls the page down. Without the fix it fails with expected +0 to be above +0.

Both pass with the fix. I ran the full suite in Chrome with web-test-runner --config test/web-test-runner.config.mjs and CHROME_PATH set (--concurrency 1): 1777 passed, 0 failed, 3 skipped. I couldn't use npm run test because the Playwright browser build it expects isn't installed on this machine.

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for
  source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly
  approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded