Make CSS is animatable data consistent

[chrisdavidmills]

Summary

As per #30358 (comment), This PR aims to make CSS data more consistent in cases where a feature (property or type) started its life off not animatable, but was made animatable later on.

In such cases, I am using the following keys:

• is_animatable when the data point describes when the feature was made @keyframe animatable, or @keyframe animatable and transitionable.
• is_transitionable when the data point describes when the feature was made transitionable.

And the following description structure:

• "@keyframe animatable" when the data point describes when the feature was made @keyframe animatable.
• "Transitionable" when the data point describes when the feature was made transitionable.
• "@keyframe animatable and transitionable" when the data point describes when the feature was made @keyframe animatable and transitionable.

The description also has an optional suffix: "when x", where x is a particular condition under which the feature is animatable and/or transitionable. For example — "@keyframe animatable and transitionable when setting inset properties"

Notes:

• text-combine-upright started off animatable in Fx, but that was a mistake, and it was corrected per spec later on. I don't think this is worth adding a separate data point for, so I've just left that one as a note.
• I've not added a guideline for this yet, as I'm not sure where to do that. I am hoping the above will for the basis of that.

Test results and supporting details

Related issues

[github-actions]

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[ddbeck]

Thanks for starting this, Chris! I think this will be a nice improvement. I've got one inline suggestion.

Additionally, I'd say that I don't love the @keyframe text, though I don't feel super strongly about it. I kinda think "Animatable and transitionable" gets the point across, but maybe others will have a different take.

For the guideline text, that will need to go into a new file: docs/data-guidelines/css.md. It'll look something like this:

# Data guidelines for CSS features

This file contains guidelines that are specific to CSS features (`css/`).

## Animatable and transitionable

Use the key name `is_animatable` to…

<!-- whatever else you have to say here, ideally imperative mood -->

This guideline was proposed in [#30417](https://github.com/mdn/browser-compat-data/pull/30417/).

There will be just one guideline in it, to start. That's fine.

[ddbeck]

AFAICT, the only difference here is between Chrome 116 and 117, so I think here we ought to have one "normal" is_animatable feature, where Chrome is partial at 116 and fully implemented at 117.

If that makes sense, we can dispense with the special case of is_transitionable.

[chrisdavidmills]

This is a nice idea. I've had a go at updating it.

Notes:

• On the 116 partial data, I've put a note "@keyframe animatable only"
• For the overall description, I've put a slightly different form than previous ones we've discussed — "@keyframe animatable; transitionable when setting transition-behavior: allow-discrete". This is because the keyframe animatable part doesn't require transition-behavior: allow-discrete to be set, but transitions do. I didn't want people thinking transition-behavior: allow-discrete was required for both.

[chrisdavidmills]

Additionally, I'd say that I don't love the @keyframe text, though I don't feel super strongly about it. I kinda think "Animatable and transitionable" gets the point across, but maybe others will have a different take.

The @keyframe bit looks slightly messier and wordier, but I think it is useful just to make it clear what kind of animations we are talking about. Some people think @keyframe animations and transitions are interchangeable, some people might think we are talking about SVG or even JS animations.

Maybe it's not that important. Perhaps we should get a third opinion on this.

[chrisdavidmills]

For the guideline text, that will need to go into a new file: docs/data-guidelines/css.md.

I've added the data guideline too.

[ddbeck]

I'm happy with this, but this needs more eyes from owners. I've put it on the agenda for the next BCD meeting.