JakeQZ

This issues from the last review should all now be resolved.

> Though browsers have a `Content-Type` header that may include a `charset=` specifier that we don’t have (as well as the resolved charset of the referring document). We can use...

It's already private, so we can do this without any deprecation issues.

OTOH, there are the `getRule` and `setRule` methods, which would need corresponding `getPropertyName` and `setPropertyName` replacements, and a deprecation notice for the originals saying to use the replacements.

> When we implement the trait, we don't need to add it to the `@covers` annotations of the corresponding testcases as PHPUnit [includes them automatically starting with version 7.3](https://github.com/sebastianbergmann/phpunit/commit/7372585bdc9a4cc1f710d5d447babd30c7b8072e). Presumably...

> * I'm a big fan of adding comments to add traits only if there also is a corresponding interface (or to create the corresponding interface), and to add a...

> anonymous class defined in `setUp()` This can implement `Commentable` so it has a defined type (rather than just `object`).

> I'd be fine with either `getObjectForTrait` or a fixture class in `tests` that uses the trait. (I'd slightly prefer the latter.) `getObjectForTrait` is not on the menu, since we'd...

We also have some in Emogrifier: https://github.com/MyIntervals/emogrifier/blob/main/tests/Unit/CssInlinerTest.php#L1123-1317

This shouldn't be too tricky to implement. These are my initial thoughts: - `RuleSet::$rules` elements would need to be allowed to be either a `Rule` or a `DeclarationBlock`: - A...