IDC's versus Egyptian format controls

[James Kass via Unicode]

I apologize for apparently misunderstanding the scope of what was
being proposed.

If a finite set of unencoded Han characters needs to be displayed
correctly using IDSes, then the complexity of the look-up tables
depends upon how many characters are in the set.  It would probably
best be handled at the font level and we shouldn't expect any
mainstream support.

If any reasonable IDS is expected to be displayed as a Han ideograph,
then the project would be vast.  It's doable and I'm sure there would
be several approaches.  It would not be feasible at the font level.

I agree that the language in the text cited earlier in this thread
should be strengthened to clarify that visible display of the IDCs is
expected behavior while enabling higher level protocols to remain
conformant if they attempt to display constructs in place of IDSes.
But I don't think that the fact that a previously unencoded character
has become encoded should forbid any application from making a display
substitution based on IDSes.