The openmonitor() function will locate and open the requested monitorspec.
It is called with either the name of the monitor or a ModeID.

    mspc = struct MonitorSpec *OpenMonitor(STRPTR name, ULONG modeID)

If the name argument is non-NULL, the monitorspec is chosen by name.  if
the name argument is NULL, the MonitorSpec is chosen by ModeID.  If both
the name and ModeID arguments are NULL, a pointer to the MonitorSpec for
the default monitor is returned.  openmonitor() returns either a pointer
to a MonitorSpec structure, or NULL if the requested MonitorSpec could not
be opened.  The closemonitor() function relinquishes access to a
MonitorSpec previously acquired with OpenMonitor().

To set up a view in release 2, a viewextra structure must also be created
and attached to it.  The ViewExtra.Monitor field must be initialized to
the address of a valid monitorspec structure before the view is displayed.
Use openmonitor() to initialize the monitor field.