Fwiw, no browser supports text-align-last: match-parent.

@fantasai Do you know where this was added?

Isn't this defined in https://drafts.csswg.org/css-text/#valdef-text-align-match-parent ?

This value behaves the same as inherit (computes to its parent’s computed value) except that an inherited value of start or end is interpreted against the parent’s (or the initial containing block’s, if there is no parent) direction value and results in a computed value of either left or right.

The behavior would be like for text-align-all, but for the last line.

Isn't this defined in https://drafts.csswg.org/css-text/#valdef-text-align-match-parent ?

This value behaves the same as inherit (computes to its parent’s computed value) except that an inherited value of start or end is interpreted against the parent’s (or the initial containing block’s, if there is no parent) direction value and results in a computed value of either left or right.

The behavior would be like for text-align-all, but for the last line.

That's for text-align. What is the parent of the last-line? Also it doesn't explain why the computed value of match-parent is as specified for text-align-last, but not text-align (where match-parent computes to left/right).

That's for text-align.

But in the spec text-align is a shorthand, so text-align: match-parent just sets text-align-all: match-parent and text-align-last: match-parent. Defining values in shorthands seems confusing to me, but it also happens e.g. in https://drafts.csswg.org/css-overflow/#propdef-overflow

What is the parent of the last-line?

It's not the parent of the last line. If the block container is element-generated, then it's the parent element of the element that generates that block container. If it's anonymous, it's the parent box of the block container (see https://drafts.csswg.org/css-display-3/#anonymous).

The root element has no parent. So the inherited value is the initial value, start, which is then resolved using the direction of the initial containing block, which per https://drafts.csswg.org/css-display-3/#containing-block is the direction of the root element itself. Not sure if this is the computed or the used value, which may be different due to https://drafts.csswg.org/css-writing-modes-4/#principal-flow. Whatever happens, it should be analogous for text-align-all and text-align-last.

Also it doesn't explain why the computed value of match-parent is as specified for text-align-last, but not text-align

Yeah, I guess text-align-last should also say "Computed value: keyword as specified, except for match-parent which computes as defined above".

@nt1m Given Oriol's explanations and the edits, do we need any further edits here?

Sounds good.