iCal Attachment Format ?

Hi all! Built an appointment scheduling app, but now the client wants it to send out an email with the appt attached in iCal format. I've never dealt with anything iCal before. I searched around a bit, and know that there iCal php scripts available, but I don't need a bunch of rigamarole, just need to create the attachment and send it on the fly. But I'm having trouble finding the format. Anyone know what this looks like? Or can point me to a resource? Rather not scrounge thru someone else's code, or have to install something just to run it for the format...if I can help it. :) Thank you, Jason