An overview of the design of XAS is presented elsewhere and is available on line at http://sax.iasf-milano.inaf.it/Sax/xasblurb.html.
A presentation of XAS has been made at the 5th International Workshop on "Data Analysis in Astronomy" (Erice, Oct 27-Nov 3 1996) and a compressed PostScript version of the paper is available (also PDF). XAS has been distributed internally to the SAX consortium since 1992 care of ITESRE . With the establishment of SAX SDC the task of distribution to the public has been assigned to the latter institution.
It is planned to add in a more or less near future also a HTML XAS Programmers manual : watch this space.