textinsert.extension — Enables the textinsert extension element
The textinsert extension element inserts the contents of a file into the result tree (as text).
To use the textinsert extension element, you must use
        either Saxon or Xalan as your XSLT processor (it doesn’t
        work with xsltproc), along with either the DocBook Saxon
        extensions or DocBook Xalan extensions (for more
        information about those extensions, see DocBook XSL: TCG, DocBook Saxon Extensions and DocBook XSL: TCG, DocBook Xalan Extensions), and you must set both
        the use.extensions and
        textinsert.extension parameters to
        1.
As an alternative to using the textinsert element,
        consider using an Xinclude element with the
        parse="text" attribute and value
        specified, as detailed in DocBook XSL: TCG, Using XInclude for text inclusions.
You can also use the <?dbhtml-include href?> processing
      instruction to insert external files — both files containing
      plain text and files with markup content (including HTML
      content).
For how-to documentation on inserting contents of external code files and other text files into output, see DocBook XSL: TCG, External code files.
For guidelines on inserting contents of HTML files into output, see DocBook XSL: TCG, Inserting external HTML code.