[mh] "Voice" commands with arbitrary parameters

I'm diving into so-called voice commands for the first time, though I'm 
really just using mhsend to send a command from another computer. The 
basics work fine, but in one case I'd like to pass an arbitrary file 
name, and have my code receive that file name. Something like "play file 
<filename>" and have my code be able to retrieve whatever was specified 
for <filename>. Can that be done, and if so, what's the syntax to define 
the voice command with an arbitrary string?

                      -Brian M.