[css-fonts] Improve implementation guidance for font-kerning
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Description
The CSS Fonts spec says that when kerning is enabled (i.e. with font-kerning: normal, or with the initial auto value "at the discretion of the user agent"), the OpenType 'kern' (horizontal) or 'vkrn' (vertical) feature should be applied.
In https://bugzilla.mozilla.org/show_bug.cgi?id=1797431, the reporter points out that the OpenType feature registry says that
If 'kern' is activated, 'palt' must also be activated if it exists.
Similarly, 'vpal' is supposed to be applied along with 'vkrn'.
Current browser engines appear to have overlooked this, and by default apply 'kern' but not 'palt' in the reporter's testcase.
I'd suggest it would be helpful to mention these associated features in the CSS Fonts description of how kerning is implemented when using OpenType fonts.
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 CSS Fonts font-kerning section linked in the issue, then compare its OpenType guidance with the cited 'kern', 'palt', 'vkrn', and 'vpal' registry entries. Update the specification guidance to mention the associated features, and consider the work done when the section accurately reflects those relationships.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- css
- Domain
- documentation
- Issue type
- Documentation
- Difficulty
- 2/5
- Estimated time
- 1-3 hours
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 48/100