From what I can tell, it basically includes the JavaScript to run, and then the main program tells it which engine to feed it to. From some issue tracker discussion, it does the latter in the common way of "look up an executable on $PATH or use a user-provided path, and shell out to it". I didn't check where the logic is located for building the command line needed for each supported engine.
Hmm! Close enough, I guess. I didn't notice that. But I hope that it has a flexible interface and that all projects adopt it.
From what I can tell, it basically includes the JavaScript to run, and then the main program tells it which engine to feed it to. From some issue tracker discussion, it does the latter in the common way of "look up an executable on $PATH or use a user-provided path, and shell out to it". I didn't check where the logic is located for building the command line needed for each supported engine.