This PR adds a new `in-*` variant that allows you to apply utilities
when you are in a certain selector.
While doing research for codemods, we notice that some people use
`group-[]:flex` (yep, the arbitrary value is empty…). The idea behind is
that people want to know if you are in a `.group` or not.
Similarly, some people use `group-[]/name:flex` to know when you are in
a `.group/name` class or not.
This new `in-*` variant allows you to do that without any hacks.
If you want to check whether you are inside of a `p` tag, then you can
write `in-[p]:flex`. If you want to check that you are inside of a
`.group`, you can write `in-[.group]`.
This variant is also a compound variant, which means that you can write
`in-data-visible:flex` which generates the following CSS:
```css
:where([data-visible]) .in-data-visible\:flex {
display: flex;
}
```
This variant also compounds with `not-*`, for example:
`not-in-[.group]:flex`.
Additionally, this PR also includes a codemod to convert `group-[]:flex`
to `in-[.group]:flex`.
---
This was proposed before for v3 in #13912
---------
Co-authored-by: Eloy Espinaco <eloyesp@gmail.com>
Co-authored-by: Jordan Pittman <jordan@cryptica.me>
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