M4 macros for configuring R are contained in subdir `m4'.

These files are used by a program called aclocal (part of the GNU
automake package) which uses them to create aclocal.m4 which is in turn
used by autoconf to create the configure script at the the top level in
this distribution.

(Actually, as we need to change a few `standard' macros, we need to
create acinclude.m4 by concatenating all m4 files in this directory
before running aclocal.)

See `m4/README' for more information about the individual files.

Hence, changes to the M4 macros *must* be made in subdir `m4', or will
be lost the next time `acinclude.m4' or `aclocal.m4' are rebuilt.  If
`--enable-maintainer-mode' was given, a change in one of the macros will
correctly rebuild acinclude.m4, aclocal.m4 and configure when make is
invoked in the top builddir.