{A..z} brace expansion in Bash 3

[Oliver Kiddle]

It does things like this:
$ echo {Z..a}
Z [  ] ^ _ a

I wouldn't see a problem if it allowed things like this:

$ echo {_..c}
{_..c}

How does it decide what characters are allowed. The following really
looks like a bug to me:
$ echo {Ä..D}
That's accepted and produces output that seems to wrap round to ^A and
then goes up to D. Note that I'm using an ISO-8859-1 locale. If that
works at all, it should surely descend.

Note that zsh has a braceccl (brace character class) option which does
the same sort of thing but differently. Other ideas for more sensible
behaviour would be to only allow A-Z or a-z ranges (not mixing). Or is
something using locale collation sequences possible.

Oliver