T.61 -> Unicode conversion

[Hallvard B Furuseth <h.b.furuseth@usit.uio.no>]

As far as I can tell, X.500/LDAP servers and X.500<->LDAP gateways may
use another mapping between T.61 and Unicode than the one in [Strprep]
Appendix A for transfer and storage of values, *except* for string
matching, for which [Strprep] section 2.1 says:

  TeletexString [X.680][T.61] values are transcoded to Unicode as
  described in Appendix A.

Though I don't quite understand when this sentence applies.  Only for
X.500/LDAP servers and when transferring values in binary format over
the protocol?

Can it happen that a Modify operation contains an UTF-8 value which
according to Appendix A does not match an existing value in the entry,
but which the server stores as a T.61 value which does match an existing
value?

Unless I'm confused about this, Appendix A shouldn't apply to just
string matching but to converting T.61 strings to Unicode in general.


Also,

I'm pretty sure that when I used X.500 and T.61 (10+ years ago?), at
least the T.61 Underline combining character could be combined with
other combining characters.  I don't know if Unicode allows that; the
strprep description of doing so at the end of Appendix A does not.

Also, I may remember wrong but there seems to be a lot more valid
character combinations (accent character + other character) than there
was in the T.61 I am used to.  Does the strprep algorithm accept any
T.61 character combination which can be mapped to Unicode, whether or
not the combination is valid in T.61?  If so, there are strings which
Stringprep will incorrectly will treat as valid.

I don't know where to find T.61 so I can check this, though.  At least
not on a Sunday:-)

-- 
Hallvard