DocBook is a widely-used format for writing documentation, articles, books, etc. Easiest way to generate HTML is to use xsltproc.
You need to install the following packages in Debian/Devuan:
apt-get install xsltproc docbook-xsl-ns docbook5-xml
Then run xsltproc as below and it will create an HTML file (documentation.html in this case) in the current directory:
xsltproc -o documentation.html /usr/share/xml/docbook/stylesheet/docbook-xsl-ns/html/docbook.xsl documentation.xml