x86 instruction emulation backstory?

[Alex Olson <this.is.a0lson@xxxxxxxxx>]

I've been digging into VMX internals and I see why MMIO emulation pretty much
requires x86 instruction emulation.  Even the Linux KVM code borrowed Xen's
emulation...

Thus, I'm trying to understand Xen's x86 emulation implementation...

How was it developed? (x86 instruction handling is incredibly complex!) 

Was it originally part of a general purpose x86 emulator?  

It looks like it implements more instructions than just ones that can access
memory, such as "AAM"?  (Why is this)?

Thanks

-Alex