The non-public version of this book was written in HTML & CSS and offered to anyone who emailed me (Pabs), & several people took up this offer. This DocBook version was converted from the HTML version using HTML Tidy and a slightly customised version of the Html2DocBook XSL stylesheet (written by Jeff Beal) found on the DocBook Wiki. The raw output was then edited (using SciTE and occasionally emacs/psgml) to look nice, change the bridgeheads into proper sections and add some DocBook markup. The old HTML versions will also be available for anyone wanting to see the early history of this project.