[Regexp] Collation elements

Hi

Confused here with multi character collating elements.
I keep reading the man pages, MYSQL documentation, etc that the 
following should result in at least a match:
[[.ch.]]*c  chchchc
However the GNU regex.h include in my test program and the MySQL statement:
SELECT xField from x where xField regexp "[[.ch.]]"  (the field in 
question containing chchchc)
fail to compile. As far as I understand, this should be valid syntax.
Whats wrong here?

Thank for any help
Buggy