Defer 'align' behavior to CSS via 'justify-items: legacy'

[fantasai]

https://html.spec.whatwg.org/multipage/rendering.html#the-css-user-agent-style-sheet-and-presentational-hints

When a user agent is to align descendants of a node, the user agent is expected to align only those descendants that have both their 'margin-inline-start' and 'margin-inline-end' properties computing to a value other than 'auto', that are over-constrained and that have one of those two margins with a used value forced to a greater value, and that do not themselves have an applicable align attribute. When multiple elements are to align a particular descendant, the most deeply nested such element is expected to override the others. Aligned elements are expected to be aligned by having the used values of their margins on the line-left and line-right sides be set accordingly. [CSSLOGICAL] [CSSWM]

The CSS Box Alignment spec added a legacy value to justify-items to handle the block-level behavior of the HTML align attribute (when it is used for alignment rather than floating): https://drafts.csswg.org/css-align/#justify-items-property It seems its being implemented, so maybe HTML can update to use that instead of defining magic behavior. (You'd need to declare both justify-items and text-align on the element triggering alignment; text-alignment and block-alignment are independent effects in CSS.)

[annevk]

From the blink-dev thread I got the impression that it was only implemented for Grid Layout, not as a generic, and therefore wouldn't end up working here.

[fantasai]

It's defined to work in block layout, so it should eventually work . If it's not the intention of HTML to use this feature, then it should be removed from CSS. Please let me know if this is the case.

[annevk]

We'd use it if it gets implemented, tested, and browsers remove the bits they currently have in place. I'd rather not remove the current prose until that is all a bit clearer.