It didn't take me long to find
this link. The document confirms what you said, namely
"Unfortunately, there is very little online information to link to about Mezzanine, as it really predates the advent of the popular Web. Its technical audience has traditionally been large organizations, hence the primary mode of information transfer has always been classes given by Saros/FileNET or by third parties, and no technical information is really accessible online."
So I would suggest looking for printed documentation or asking your sales person. I wouldn't really expect to find a Java API given the age and obsoleteness of the product.
[ February 10, 2006: Message edited by: Paul Clapham ]