This document is an attempt to specify the XBRA protocol for exception
vector chaining on the atariST series of computers. It is a response
to many requests I have received to document the protocol, and also an
encouragement for people grabbing exception vectors to use it. This protocol
was not invented by me, nor is it perfect for every situation, but
still is very useful because something is better than nothing. There
have been other proposals, but IMHO this is the simplest and cleanest,
and does the job for which it was designed quite well. It has been
used quite widely, especially in Public Domain circles, and that is a
good enough reason for me to follow it.