The original text were published by Cambridge Computer in 1988, which could be bought separately or as part of a commercial Z88 application development kit. Matthew Soar has since then published them here: http://www.cix.co.uk/~ponda/Z88dev093.htm.
25th October 2015: Final authoring of V4.6 edition ongoing.
9th July 2015: Progress of final authoring of V4.5 edition ongoing. First works have been added for OZ V4.6 API.
8th June 2014: Updated API for OZ V4.5
26th May 2012: 98% of the notes are now imported and improved with better text-layout. A few chapters have yet to be imported and links to System Call API's are currently being applied everywhere in the text.