xmlto is a front-end to an XSL toolchain. It chooses an appropriate
stylesheet for the conversion you want and applies it using an external
XSL-T processor.  It also performs any necessary post-processing.

Supported conversions from DocBook XML: dvi, fo, html, html-nochunks,
htmlhelp, javahelp, man, pdf, ps, txt, xhtml, xhtml-nochunks.

Currently the only XSL-T processor supported is xsltproc (textproc/libxslt).
For DVI, PDF and PostScript output, PassiveTeX (print/passivetex) is required.