Accessing marked regions in ZMACS

[Keith Ackley <ACKLEY%kbs2.tamu.edu@RELAY.CS.NET>]

I have a command in ZMACS where the user marks a region of text,
and then types a single keystroke to invoke the command. The
problem is how do I access that section of text in my command.
Is there some easy way to open a stream on that interval?

I have found the function OPEN-INTERVAL-STREAM which appears to
be what I want. But how do you specify the region that has
been marked by the user.

                          Keith Ackley