https://github.com/w3c/csswg-drafts/issues/7656 contains a conversation regarding baselines for field sets. It doesn't appear to be in the spec yet, but we can expect to see it updated with the information in the comments. The following tests are for this behavior: grid-align-baseline-fieldset-001.html grid-align-baseline-fieldset-002.html grid-align-baseline-fieldset-003.html
<rdar://problem/101087442>