N is the width of the box in average characters. M is the number
of lines in the control which will include a scroll bar if M is not
options can be omitted or can take the value sorted to specify that the
parameters are to be alphabetically sorted by name.
After a parameter block has been defined parameters can be attached by
subsequent formats thus:
%dp - Integer parameter
%fp - Floating point parameter
%tp - Text parameter
%ep - Enumerated parameter (a set of named alternatives)
%up - User parameter (just activates a call-back)
Each of these codes is followed by a standard character string that
provides the text to be displayed. See
Parameter box for further information.