JavaScript/Webcal - Protocol detection?

Question

I'm getting ready to release an iCal subscription feature, and I'd like to set the protocol to https:// or webcal://, depending on browser support. I'm aware that webcal is an unofficial protocol, but is there a way I can check if the browser supports it? So far nothing seems to make it work in IE8, and I'm about to test IE9+, but I'd prefer to offer graceful degradation for all browsers that don't understand webcal:// (as I understand it, the Android browser also appears to have issues with it).

Deerskin