# Root nodes and conditional tagging

If the root node of an XML file is excluded with a conditional, your document will not build, because empty files are not valid XML. For example, if `Installation_and_configuration_on_Fedora.xml` contains a single chapter:

    <?xml version='1.0' encoding='utf-8' ?>
    <!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
    ]>
    <chapter id="chap-Installation_and_configuration_on_Fedora" condition="Fedora">
    <title>Installation and configuration on Fedora</title>

    [text of chapter]

    </chapter>

and this chapter is included in `User_Guide.xml` with an `<xi:include>` tag, the document will not build with $ `condition: Ubuntu` set in the `publican.cfg` file.

To exclude this chapter, add a condition to the `<xi:include>` tag in `User_Guide.xml`, not to the `<chapter>` tag in `Installation_and_configuration_on_Fedora.xml`.