tcl/tk and Javascript only support UCS-2 (16 bit) Unicode strings.
Dealing with the Supplementary Unicode Planes have the same problems
that older "narrow" builds of Python sufferred from: single code points
were counted as len(2) instead of len(1), slicing could be wrong, etc.

There are still many applications which assume Latin-1 data. For
instance, I use a media player which displays mojibake when passed
anything outside of Latin-1.

Sometimes it is useful to know in advance when text you pass to another
application is going to run into problems because of the other
application's limitations.