[dev-context] Font switching in XeTeX

Hello Hans and Adam, Which are the high-level font switching commands for XeTeX? Documentation in font-ini states that something like \definedfont["cmtt10" at 40pt] should work, but if I try to play with \definedfont["Latin Modern Roman" at 40pt] I get the message that TFM files for "Latin Modern Roman" do not exist. \font\A="Latin Modern Roman" at 40pt works OK. I have some problems with the default Type1 lmr font - it doesn't know that there are any "ccarons" present in the font (with OpenType lmr it works OK), but I have to inspect that a bit anyway. There should be a way to "preload" the lm fonts so that they would work OK with diacritical marks. Mojca