Syntax highlighting

The customisation enables the option in the DocBook XSLT 1.0 Stylesheets to perform syntax highlighting on program listings using the XSLTHL syntax highlighting utility. [XSLTHL]

XSLTHL feels like a good fit for use with XSLT because it is an extension function for the XSLT processor, it does not require any other programming language, and its configuration files are XML. In reality: it is quite old; development on SourceForge had stalled and no new languages had been added for several years; it only works with Xalan, Saxon 6.5, and SaxonB (up to around Saxon 9.1) and only on Java.[15]

Highlighters for XQuery, DTDs and batch files were added to the XSLTHL project on GitHub to handle more formats used in the papers.

[15] Antenna House has contributed a PR that lets XSLTHL work with Saxon versions up to 9.9, but that is not in any official release.