-Pass extra flags to zeromq's F<configure> script. You may want to consider
-passing either C<--with-pgm> or C<--with-system-pgm> if you need support for
-PGM; this is not enabled by default because it is not supported by every
-system.
+Pass extra flags to the compiler when probing for an existing installation of
+libzmq. You can use this, along with L</--zmq-libs>, to help the probing
+function locate your libzmq installation if it is installed in an unexpected
+place. For example, if your libzmq is installed at F</opt/zeromq>, you can do
+something like this:
+
+ perl ./Build.PL --zmq-cflags="-I/opt/zeromq/include" \
+ --zmq-libs="-L/opt/zeromq/lib -lzmq"
+
+These flags are only used by the probing function to locate libzmq; they will
+not be used when compiling libzmq from source (if it needs to be). To affect
+the compiling of libzmq, using the L</--zmq-config> flag instead.