I am looking at this:
The possible values are lrt, rtl, and auto
(with auto "determined heuristically, based on the first strong directional
character in scope, see UAX #9").
That is the same as the HTML dir attribute
But that is not enough, because the direction based on the first char
results in bad rendering at times.
So the HTML standard added <bdi> and <bdo>
And also CSS needed to add even more control, with unicode-bidi:
The values in the CSS2 standard seem to be normal, embed, bidi-override,
But more are coming: normal, embed, isolate, bidi-override,
Mozilla and Chrome (and probably others will follow) already support these
Chrome also supports "initial" (I don't check about Firefox)
So the proposed values for dir seem insufficient.
Kind of a pity to release something that is already outdated, without
learning from what others did...