xLIB is built-in Celtic III (along with two Omnicalc commands) and Celtic III is built-in Doors CS7. Celtic III doesn't emulate xLIB properly, though, unlike Doors CS7.

As for hybrid TI-BASIC, it's when you combine TI-BASIC language with ASM libraries such as Doors CS7, Omnicalc, CODE X, XCOPY, Celtic III, xLIB, etc. ASM libraries allows you to do things you cannot do with pure TI-BASIC code, while not forcing you to learn assembly. An example of hybrid TI-BASIC would be this: