[css-view-transitions-1] View Transition on a fragmented inline

[khushalsagar]

We resolved that fragmented elements should be ignored by View Transition here: #8339 (comment). But its not clear whether this resolution also covers inline-box fragmentation across line boxes. The spec is limited to box fragmentation : If element has more than one box fragment, then continue..

So filing this issue to resolve on the behaviour for inline fragmentation.

IIRC we resolved on ignoring box fragmentation because:

1. The position model was very hard to define. If a fragmented box has a transform it individually applies to each fragment. So unioning all the fragments to generate an image and then applying the transform on top of this image (which is how View Transition works) wasn't feasible.
2. There are plans to make each fragment addressable in CSS via pseudo-elements like nth-fragment in which authors can add a view-transition-name to any fragment.

1 is not a concern for inlines because transform property doesn't apply there. So we could consider an approach of unioning all line box fragments here.

2 is interesting in that you can already target the first line box via ::first-line.

@fantasai @tabatkins any advice on this?

[khushalsagar]

Fixed with #9581. The spec aligns with intended behaviour so I added a non-normative note to avoid ambiguity.