Never really thought about it i guess, i just figured mirc kept it in memory and scanned through it that way. Still, mirc would need an internal recuring timer of its own to do something to handle idle events, couldn't hurt to require the user to create this timer so that more control can be had over the event without needing to edit the script itself.
Does make more sense that mirc would create and release binds in that way rather than parsing the data all the time.
