der Mouse  <mouse@Rodents.Montreal.QC.CA> writes:

  >> arg='&foo'
  >> case "$arg" in
  >> *[\[\]\&]*)

  > That expression matches
  > 	*	zero or more characters
  > 	[\[\]	same as [[] - an open bracket
  > 	\&	an &
  > 	]	a close bracket
  > 	*	zero or more characters
  > which does not match "&foo".

This code is from autoconfig and works in bash.  That, of course, is
no guarantee it is correct!

  > There may be a bug, but if so it's in quoting, not matching.  ] is not
  > considered to be a character that needs quoting, so attempts to quote
  > it get stripped, and by the time it makes it down to the routine that
  > matches [...] character classes in glob patterns, any record of it
  > having been quoted has been destroyed.  Read the "Shell Patterns"
  > section in the sh manpage (at the top of page 19); ] is not a
  > meta-character - or, to put it another way, a character class opened by
  > [ extends up to the next ] *regardless of whether the ] is quoted*
  > (with a special case to allow putting ] into a class by listing it
  > first).

Sounds like the bug is in autoconf. Thanks for the analysis.

Ian