There's an odd inconsistency among the values defined for the position-area property:

https://drafts.csswg.org/css-anchor-position-1/#position-area-syntax

Specifically, for the self-* logical keywords which refer to the box’s own writing mode (rather than the containing block's), the addition of "self" to the value is done inconsistently. So for example, the own-writing-mode version of inline-start is self-inline-start (with "self" as a prefix), but the own-writing-mode version of x-start is given as x-self-start (with "self" as an infix).

IMO this is unnecessarily confusing/illogical and will be an annoyance to authors. We should make "self" a prefix in all cases (as is done with "span"), not sometimes a prefix and sometimes an infix.

I propose, therefore, the following renaming of values:

x-self-start -> self-x-start
x-self-end -> self-x-end
y-self-start -> self-y-start
y-self-end -> self-y-end

span-x-self-start -> span-self-x-start
span-x-self-end -> span-self-x-end
span-y-self-start -> span-self-y-start
span-y-self-end -> span-self-y-end

As far as I'm aware, nobody has yet implemented these values, so renaming them to follow a more consistent pattern should not carry any compatibility risk.