[css-align-3] Do the CSS2.1 rules apply for determining the last-baseline of flex/grid/etc ?

[bfgeek]

CSS2.1 has a "fun" rule:

https://www.w3.org/TR/2011/REC-CSS2-20110607/visudet.html#q10.0
"The baseline of an 'inline-block' is the baseline of its last line box in the normal flow, unless it has either no in-flow line boxes or if its 'overflow' property has a computed value other than 'visible', in which case the baseline is the bottom margin edge."

Does this rule impact "align-self: last baseline" ? And if so how?

For reference - Firefox appears to be setting to the block-end border-box edge when "overflow:hidden" is present.
https://www.software.hixie.ch/utilities/js/live-dom-viewer/?saved=10609

@fantasai @tabatkins

[fantasai]

We also have this CSS2.1 issue, fwiw:
#2781

So, options:

• Give first-baseline this weird behavior, take the desired behavior for last-baseline.
  • This would put the last baseline above the first in many cases.
• Give both first and last-baseline this weird behavior
  • Consistent but not awesome.
• If baseline-source is auto, do the weird thing, otherwise use the desired behavior.
  • Lets us opt out of weirdness and use the real baseline.

Desired behavior being: use the actual baseline if it's above the box’s bottom edge, and clamp it to that position if it overflows. See #7660

Either way, I don't think we need to import this weirdness into flex and grid formatting contexts.