From the Oreilly announcement: “While we would have liked to make these e-books available sooner, we felt it was important to first contribute to building some of the tools needed for other publishers to follow our lead, such as enhancements to the open-source DocBook XSL stylesheets, which can now generate EPUB from DocBook XML source files.”
Related: Open Source DocBook XSL experimental ePub support released, from O’Reilly’s TOC blog. – D.R.
Also of interest: Wikipedia item on DocBook. This markup language—semantic in nature—is of special interest to technical publishers. – D.R.
Thanks for the mention of the DocBook-XSL .epub target (included in the 1.74.0). There’s also ongoing work from the DocBook SubCommittee for Publishers (Disclosure: I’m a member) to produce a subset of DocBook 5.0 expressly for “regular”, non-technical publishers.