I found this little jewel at the floodgap retrotech site. I picked up version 2.3.5 (circa February 7, 2009) in late 2012.
Here is a link to the html documentation for version 2.1.4. The latest documentation is only in man format.
Also, xa has a companion disassembler "dxa", which looks interesting. One key feature is that it claims to do "perfect disassembly", i.e. it allows you to disassemble an object, and then be able to feed the resulting file to "xa" to get back your object. This of course has wonderful implications for somebody wanting to modify some existing firmware.
The version of dxa I found is circa June 2, 2007. The malloc patch came along in August 31, 2010, and fixes a bug in the label manager. It is supposed to be a two line change.Tom's Computer Info / tom@mmto.org