Well I figured out where to insert the short description (/components/com_dtregister/views/calendar/tmpl/index.php - around line 400, I'm wanting it after the image but before the rest of the info).
My issue now is determining what I need to put there, right now this is what I have:
if(v[24] != ""){
str += '<br /><?php echo JText::_('Description')?>: '+v[24]+'';
}
I was able to figure out that there is a variable array (as indicated by the v with a number in brackets ranging from 0 to 23) of some kind. The calendar is retrieving the information from the array and using it for each of the pop-up elements (title, img, dates, price, etc.), however I can't locate where the array is being populated. I'm guessing that I should be able to add another field onto the end of the array that would allow me to call the event_describe field from the db_dtregister_group_event table (hence the '24' in the code). I need to figure out where the variable 'v' is coming from.
Looking at the list view was somewhat helpful, though the way that it stores the database information is totally different.
I discovered most of this through trial and error, so if anyone has some insight into it I would be grateful.