Re: "sed" question

In article <tv26ck-3qt.ln1@ID-313840.user.individual.net>,
Geoff Clare  <netnews@gclare.org.uk> wrote:

POSIX requires that awk uses extended regular expressions (i.e. the
same as regcomp() with REG_EXTENDED).

There is the additional requirement that \ inside [....] can
be used to escape characters, so that [abc\]def] is valid in
awk but not in other uses of REG_EXTENDED.