The Include tool is designed to make it quick and easy inserting “XML variables” in your documents.

XML variables are often-used contents: product names, product versions, copyright information, addresses, phone numbers, etc, you need to reference in almost all your documents.

XML variables are best modelled by elements having a weak semantic and which may be inserted almost anywhere in a document. In the case of XHTML, this element is span. In the case of DocBook, this element is phrase.

XML variables are generally collected in a single, centralized, ``pseudo-document'', created for this sole purpose.

You'll insert references to XML variables, and not copies, in your actual documents.

By working this way, if one day, the value of an ``XML variable'' changes, you don't need to manually update all the documents making use of this value.

Unlike the Copy As Reference/Paste (Ctrl+Shift+C/Ctrl+V) approach described in the tutorial, which is a generic way to compose any kind of modular documents, the Include tool is specialized in XML variables. For example, do not attempt to use this tool to insert in a modular book the references to its chapters.