Bidi Mirroring and Ancient Scripts   - L2/06-071
Asmus Freytag
Feb. 9, 2006


Ancient documents often show multiple writing directions for the
same script. In Unicode, we assign a strong directionality. When
non-symmetric characters from these scripts are written in opposite
direction they are usually mirrored according to the writing direction
of the line. Our definition of the mirrored property seems to imply
that it is exhaustive. This is correct when it comes to paried
puncutation marks - it's necesary to have an either / or status here,
otherwise it's not clear which character code to put in the backing store.

This begs the question as to whether mirroring of letters for ancient
scripts (or scripts used in rendering ancient documents) is allowed
or prohibited for a conformant implementation.

Proposal

Explicitly allow a higher level protocol to mirror letters and other
characters when writing direction is overridden. Document this in
UAX#9 and 5.0.0