programme can write into and then send through the RMR library.
The buffer is allocated such that sending it requires no additional copying
out of the buffer.
-If the value passed in &cw(size) is 0, then the default size supplied on the
-&ital(rmr_init) call will be used.
+If the value passed in &cw(size) is less than or equal to 0, then the
+&ital(normal maximum size) supplied on the &ital(rmr_init) call will be used.
+When &ital(size) is greater than zero, the message allocated will have at least
+the indicated number of bytes in the payload.
+There is no maximum size imposed by RMR, however the underlying system memory
+managerment (e.g. malloc) functions may impose a limit.
+
+&space
The &ital(ctx) parameter is the void context pointer that was returned by
the &ital(rmr_init) function.