+dnl --- *@-mdw_MANEXT-@* ---
+dnl
+dnl Author: Mark Wooding
+dnl
+dnl Synopsis: mdw_MANEXT
+dnl
+dnl Arguments: ---
+dnl
+dnl Use: Sets the substitution `manext' for man page extensions.
+
+AC_DEFUN([mdw_MANEXT], [
+AC_ARG_WITH([man-ext],
+[ --with-man-ext=EXT give manpages the EXT extension (e.g., foo.3EXT)],
+[manext=$withval], [manext=mLib])
+AC_SUBST(manext)])
+