It currently is not implemented.
<rdar://problem/22959741>
Myles started implementing this is bug 148413. Currently we support: font-variant-alternates: normal | historical-forms Whereas the spec has: normal | [ stylistic(<feature-value-name>) || historical-forms || styleset(<feature-value-name>#) || character-variant(<feature-value-name>#) || swash(<feature-value-name>) || ornaments(<feature-value-name>) || annotation(<feature-value-name>) ]
Pull request: https://github.com/WebKit/WebKit/pull/4926
Committed 255201@main (96c123ec8040): <https://commits.webkit.org/255201@main> Reviewed commits have been landed. Closing PR #4926 and removing active labels.