-Matches IP protocol type \fIproto\fR, which is specified as a decimal
-number between 0 and 255, inclusive (e.g. 6 to match TCP packets).
-
+When \fBip\fR or \fBdl_type=0x0800\fR is specified, matches IP
+protocol type \fIproto\fR, which is specified as a decimal number
+between 0 and 255, inclusive (e.g. 6 to match TCP packets).
+.IP
+When \fBarp\fR or \fBdl_type=0x0806\fR is specified, matches the lower
+8 bits of the ARP opcode. ARP opcodes greater than 255 are treated as
+0.
+.IP
+When \fBdl_type\fR is wildcarded or set to a value other than 0x0800
+or 0x0806, the value of \fBnw_proto\fR is silently ignored.
+.
+.IP \fBnw_tos=\fItos\fR
+Matches IP ToS/DSCP field \fItos\fR, which is specified as a decimal
+number between 0 and 255, inclusive. Note that the two lower reserved
+bits are ignored for matching purposes.
+.IP
+The value of \fBnw_proto\fR is silently ignored unless
+\fBdl_type=0x0800\fR, \fBip\fR, \fBicmp\fR, \fBtcp\fR, or \fBudp\fR is
+also specified.
+.