> On TTY frames the tab bar is not a window, so what I wrote is impossible,
> and thus avoiding the 'right' part in the align-to spec is a good idea
> regardless.

Avoiding the 'right' part in align-to has such a drawback that while
resizing the frame the position of the aligned element is not updated
immediately.  It's updated only when display-time refreshes the time on
the tab bar.  The position relative to the right edge has no such problem.
So better to leave the 'right' part on GUI frames, and switch to counting
from the left only on TTY frames where frames are resized less often: