@dholbert pointed out in #1432 (comment) #1432 (comment) and https://bugzilla.mozilla.org/show_bug.cgi?id=1682641#c9 that the newer CSS Positioned Layout model for handling the alignment properties and the flexbox spec conflict on a few points.

First, overall:

• css-position defines abspos layout as creating an inset-modified containing block (where some of the insets are auto insets derived from the static position), and then applying alignment within that rectangle. It defines the auto offsets for a flex child to coincide with the content edges of its container.
• css-flexbox sets the position of an abspos child more directly in https://drafts.csswg.org/css-flexbox/#abspos-items in normative prose by defining it as the position the item would have had as the sole flex item (but says something different, matching css-position, in the note in the same section).

A few places where this matters that @dholbert pointed out:

• Per css-position, in a column flex container, the align-self property will apply in the block axis, not the main axis. But per css-flexbox, it will affect the static position in the main axis.
• Per css-position, the justify-self property will affect the static position in the inline axis. Per css-flexbox, it can have no effect.
• Per css-position, justify-content and align-content on the container have no effect on the child's static position. But per css-flexbox, they do.

We need to resolve these conflicts somehow.