Add mixins by new proposal

[ai]

New proposal by @tabatkins with mixins by @apply rule http://tabatkins.github.io/specs/css-apply-rule/

[MoOx]

This one require postcss v5, will add that after #202

https://github.com/pascalduez/postcss-apply

[keithamus]

For any who land here, it looks as though #208 is the new issue that needs to be resolved before this lands.

[Jcan]

Hey MoOx - we are very excited about the function. do you have a timeline for it? Thanks ;-)

[Jcan]

I think Mixin is very useful. This is a simple example:

:root {
    --clearfix: {
        content: '';
        display: table;
        clear: both;
    }
}

#header {
    ......
    &::after {
        @apply --clearfix;
    }
}

Look forward for the new feature!

[MoOx]

If someone can double check that a plugin exists and follow the spec, this should be easy to add (PR welcome, and btw, here is the way to add a feature (maybe outdated a little, but should help, it's very easy to add a new plugin) https://github.com/MoOx/postcss-cssnext/blob/master/CONTRIBUTING.md#add-a-feature)

[zeke]

Not sure I have the time or the chops to take this on, but would love to see it supported in cssnext!

[pascalduez]

The aim of postcss-apply is to follow the "spec" as close as possible, but I feel it's a bit early to name it a "spec"?
Also it's suffering the same limitations as for custom properties, no cascading or inheritance so far.
I get to make it more clear on the readme.

Anyhow, I would be happy to see it used in CSSnext.

[MoOx]

As far as the limitation does not produce any change with or without the transformation, it's not an issue. postcss-custom-properties supported code will works in modern browsers without any different behavior.

I didn't read the spec at all so I can't say anything for now (and to be honest, I am not personally interested yet by this feature, and may never be - that don't mean it does not have its place to this project).