Bug 264733 – element.checkVisibility() does not work for unslotted elements

• Status: NEW
• Component: CSS

[Max Schmitt]

https://commits.webkit.org/270425@main enabled element.checkVisibility() by default. After this the following evaluates to `true` while in Firefox and Chromium it evaluates to `false`:

```html
<details>
  <summary>Open form</summary>
  <input id="two"/>
</details>
<script>
  alert(document.querySelector("#two").checkVisibility({
    checkOpacity: false,       // default
    checkVisibilityCSS: false, // default
  }))
</script>
```

[Radar WebKit Bug Importer]

<rdar://problem/118648432>

[Tim Nguyen (:ntim)]

This was fixed for details/summary by bug 157323, but I think the issue remains for unslotted contents in general.