A configuration file is a declarative XML file which teaches XXE how to handle documents of a given type. Without an appropriate configuration file, XXE is not of much use: the opened document is rendered using a tree view, it cannot be validated, schema-directed editing does not work, the user is limited to the most basic editing commands.

XXE is bundled with configurations for DITA, DocBook and XHTML. More configurations are available but they need the user to download and install the corresponding add-on (i.e. using menu item Options → Install Add-ons).

For the impatient, the most basic configuration file looks like this:

<configuration name="Example"
  xmlns="http://www.xmlmind.com/xmleditor/schema/configuration">

  <detect>
    <dtdPublicId>-//XMLmind//DTD Example//EN</dtdPublicId>
  </detect>

  <template name="Example 1" location="example1.xml" />

</configuration>