-.IP \fB\-\-input\fR,\ \fB\-i\fR
-Specify the input file containing a list of CIDRs, rather than using
-stdin (the default).
+.IP \fB\-\-barriers\fR,\ \fB\-b\fR
+(regexed mode only) place barriers in front/back of the regex to
+prevent e.g. '127.0.0.1' from matching '127.0.0.100'. The downside is
+that the resulting regexp will match something that is not an IP
+address, and this messes up e.g. \fIgrep -o\fR.
+
+.P
+Without \fB\-\-barriers\fR, you can match things you shouldn't:
+
+.nf
+.I $ echo \(dq127.0.0.100\(dq | grep -P $(hath <<< \(dq127.0.0.1/32\(dq)
+127.0.0.100
+.fi
+
+.P
+Using \fB\-\-barriers\fR can prevent this:
+
+.nf
+.I $ echo \(dq127.0.0.100\(dq | grep -P $(hath -b <<< \(dq127.0.0.1/32\(dq)
+.I $ echo $?
+1
+.fi
+
+.P
+But, this may also cause the regex to match something that isn't an IP
+address:
+
+.nf
+.I $ echo \(dqx127.0.0.1x\(dq | grep -Po $(hath -b <<< \(dq127.0.0.1/32\(dq)
+x127.0.0.1x
+.fi