I've written and edited books in a format called PseudoPOD for many years now. My company has several tools to validate and emit other formats, including XHTML,

I've written and edited books in a format called PseudoPOD for many years now. My company has several tools to validate and emit other formats, including XHTML, LaTeX, ePub, and PDF. This works very well for us. Many of these tools are available from the Modern Perl repository on Github: http://github.com/chromatic/modern_perl_book http://github.com/chromatic/modern_perl_book