plugins/devkit/devkit-java-tests/testData/codeInsight/pluginWithXInclude.xml

<idea-plugin xmlns:xi="http://www.w3.org/2001/XInclude">

    <id>foo</id>
    <vendor>JetBrains</vendor>
    <version>1.0</version>

    <xi:include href="/pluginWithXInclude-extensionPointsWithModule.xml" xpointer="xpointer(/idea-plugin/*)"/>
    <extensionPoints>
        <extensionPoint name="bar" interface="java.util.List"/>
        <xi:include href="/pluginWithXInclude-extensionPoints.xml" xpointer="xpointer(/idea-plugin/extensionPoints/*)"/>
    </extensionPoints>

    <extensions defaultExtensionNs="foo">

        <bar implementation="java.util.ArrayList"/>
        <extensionX/>
        <extension2/>
        <<error descr="Element extensionUnknown is not allowed here">extensionUnknown</error>/>
    </extensions>

</idea-plugin>