Bug 294559 – CSS.supports('break-after', 'avoid') returns true despite no support

• Component: New Bugs
• Status: NEW

**Background**: Safari doesn't support `[page-]break-before/after: avoid`.

**Expected**: `CSS.supports('break-after', 'avoid')` should return `false`.

**Actual**: `CSS.supports('break-after', 'avoid')` returns `true`.

---

The following all return `true`, although the features aren't implemented :

```js
CSS.supports('break-before', 'avoid');
CSS.supports('break-after', 'avoid');

CSS.supports('page-break-before', 'avoid'); // legacy
CSS.supports('page-break-after', 'avoid'); // legacy
```

(`page-break-inside: avoid` and `break-inside: avoid` are omitted here, as these _are_ implemented, see bug 34080.)

---

To check, you can also run the MDN BCD Collector tests (which use `CSS.supports()` to determine support):

- break-before: https://mdn-bcd-collector.gooborg.com/tests/css/properties/break-before
- break-after: https://mdn-bcd-collector.gooborg.com/tests/css/properties/break-after
- page-break-before: https://mdn-bcd-collector.gooborg.com/tests/css/properties/page-break-before
- page-break-after: https://mdn-bcd-collector.gooborg.com/tests/css/properties/page-break-after

[Radar WebKit Bug Importer]

<rdar://problem/154095900>