Events?

Is it possible to register a callback for any events in After Effects? If so is there a reference somewhere with these events?

If not, perhaps there is another way to approach my problem? What I want to do is perform an action before export/save. My extension processes things in the composition and then stores them in the XMP metadata in a processed form. Only problem is you have to do this by opening my extensions panel and pressing a button. It all works fine but its possible to forget to press the button before you export, thus leading to old metadata being exported which isn't a great user experience.

Thanks,

Andrew.