I'm setting up a feature for "exporting as ics file" (iCal) our weekly school agenda.
The download prompt works but when opening it in iCal (Mac OS X), iCal tells me the calendar is invalid. I opened the file in a text editor and it looks ok to me. 

I suspect my download.php script is wrong or setting the wrong mimetype.

I tried `text` and `text/calendar`. No luck.

So my question is this: what's the correct mimetype for ics files?