A short comment to Randall: Well I think the EBCDIC gatewaying problem
is worse outside the US. We do have problems in Denmark with this,
all with IBM machines on the internet. Here | is turned into a !
(Broken bar/o-stroke to exclamation mark).
Another restricted character set that could be of interest
in determining "problem" characters is ASN.1 PrintableString
(ISO 8824:1987 p 21 table 5).
From ASCII the following characters are missing in PrintableString:
This adds the problem chars in addition to ISO 646 and EBCDIC
problem characters: %&*;<>_
I agree with Randall that we should not restrict ourselves too much
from these restricted character sets. But if we have the possibility,
eg. by base64 where there are a lot of characters we can discard
from ASCII, we should discard the right ones.
Another conclusion I draw is that we should avoid base85.