Sending an apple event with custom parameters (BBEdit roundtrip)

[Ben Rubinstein]

I want to send an AppleEvent with custom parameters, not covered in the 
application's dictionary.

Specifically, I want to implement BBEdit round-trip editing - which perhaps 
others have already done?

Essentially the missing piece in this is that when you invite BBEdit to open a 
document, you supply an extra parameter (keyServerID); it then knows to notify 
your application via an AppleEvent when the document is saved or closed.

However, I cannot figure out how in Transcript to add parameters to a call. 
So I can do this inside a "tell BBEdit" (all sent via "do ... as applescript):

   open "/test.txt"

or this (equivalent)

   <<event aevtodoc>> "/test.txt"

or this

   open "/test.txt" opening in new_window

or this (equivalent)

   <<event aevtodoc>> "/test.txt" opening in new_window

but I can't figure out a syntax to let me add the optional parameter without 
using the dictionary, ie something like this should be the equivalent to the 
last two above:

   <<event aevtodoc>> "/test.txt" <<property OpnI>> new_window

All the variations I've thought of give me a compiler error.  So how do I do 
that, then?

(Of course, if someone has a stack implementing BBEdit round-trip, that would 
answer this question and several others!)

TIA,

   Ben Rubinstein               |  Email: benr_mc at cogapp.com
   Cognitive Applications Ltd   |  Phone: +44 (0)1273-821600
   http://www.cogapp.com        |  Fax  : +44 (0)1273-728866