[web-animations-1] Reject old-style `:before` pseudo-element syntax
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Description
Background is the discussion in #4437.
As of that change, KeyframeEffect now has a pseudoElement member whose syntax is defined by Selectors Level 4.
That definition requires UAs to accept the old single colon syntax (:before) as well as the double colon syntax (::before).
I was under the impression we wanted to phase that historical artifact out of the web platform so that new APIs like this should reject :before and only accept ::before.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the discussion in issue #4437 and the KeyframeEffect.pseudoElement definition, then compare its syntax reference with the Selectors Level 4 pseudo-element syntax. Done means the specification clearly requires rejecting single-colon :before while accepting the double-colon form ::before.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- css
- Domain
- api, web-dev
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100