Basic program.
.IP .ocm
Occam program.
+.IP .mod
+Modula-2 module.
.IP .e
EM assembly module in human readable form.
.IP .k
When linking multiple \fI.o\fP or \fI.m\fP files created by
separate calls of \fIack\fP together, \fIack\fP cannot deduce
the run-time system needed,
-unless called as \fIapc\fP, \fIabc\fP, \fIocm\fP or \fIacc\fP.
+unless called as \fIapc\fP, \fIabc\fP, \fIocm\fP, \fIm2\fP, or \fIacc\fP.
This flag serves to tell \fIack\fP which runtime system is
needed in such a case.
For example: "ack \-c x.c ; ack \-.c x.o".