Install docbook5-xml by entering the following commands in the terminal:
sudo apt update sudo apt install docbook5-xml
standard XML documentation system for software and systems
DocBook 5 is a general purpose XML schema. That is, it contains the "DocBook" document structure. This is used by authors or editors writing documents in the DocBook XML format. DocBook was designed for books, articles, or reference documentation about technical matters or software (though it is by no means limited to these applications). It has emerged as an open standard in the software industry, and is the documentation system of choice for many free software projects. . DocBook 5.0 is a complete rewrite of the well-known DocBook 4 XML schema/DTD, introducing a quite large number of backwards-incompatible changes. But the basic idea behind DocBook is still the same, and almost all element names are unchanged. . This package contains the XML RelaxNG schema (with some additional Schematron assertions), W3C XML Schema (XSD) as well as the Document Type Definition (DTD) for DocBook, which all describe the formal structure for documents following this format. . You will need other packages in order to edit, validate (libxml2-utils) or format (docbook-xsl-ns) DocBook 5 documents.