I searched the docs, but did not find it. Some programs let you execute a script upon startup and shutdown. Does DOpus have that?
If so, I am already at my second question: I would like to extend JScript, which is ECMAScript3 with an ECMAScript5 shim, which would be my startup script. From then on, so I hope, I could use all the new objects and methods in button scripts, and alike. Or is that in contrast, to how ActiveScript hosts work?
The OnStartup scripting event is for that. Note that you cannot ensure your script runs before any others which also handle the same event.
There is also, under Preferences / Launching Opus / Startup, a place where you can specify a command to run when Opus starts. (I think that will be run later than scripts, but I'm not sure.)