Value 'default' is not legal as a custom identifier but it is not a css-wide keyword. With '*' syntax the value is just a pile of parser tokens and shouldn't be interpreted until someone tries to use it.
css/css-properties-values-api/register-property-syntax-parsing.html
<rdar://problem/104223391>
Pull request: https://github.com/WebKit/WebKit/pull/8621
Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/37941
Committed 258881@main (f5656e4975af): <https://commits.webkit.org/258881@main> Reviewed commits have been landed. Closing PR #8621 and removing active labels.