Such a file is intended to be parsed and translated by an engine (that
I will call here, a "translator") in an actual form specification/code
for building the dialog box using a particular programming language
combined with a particular graphical toolkit (Tcl/Tk, Gtk, Swing,
ActiveX/OCX,...), and possibly specialized widgets like those
currently developed for tcltk by the Bioconductor group.
This file should be very easy to build for simplest dialog boxes.
Anybody should be able to write one, and to translate it in dialog
boxes, at least, using the most automatted "translators" (this will be
obviously dependent upon the level of automatisation provided by each
translator). Of course, more complex dialog boxes, will obviously
require more work.
The ultimate level in simplicity would be to pick up any R function
and to create a specification file just by filling a dialog box asking
how each function argument should be translated into a graphical
widget (text, list, pushbuttons,...).