intellij-plugin/features/code-insight-markdown/resources/code-insight-markdown.xml

<idea-plugin>
  <dependencies>
    <!--suppress PluginXmlValidity -->
    <module name="code-insight-core"/>
    <plugin id="org.intellij.plugins.markdown"/>
  </dependencies>

  <extensions defaultExtensionNs="com.intellij">
    <completion.contributor language="Markdown"
                            id="EduMarkdownCompletionContributor"
                            implementationClass="com.jetbrains.edu.markdown.taskDescription.EduMarkdownCompletionContributor"/>
    <psi.referenceContributor language="Markdown"
                              implementation="com.jetbrains.edu.markdown.taskDescription.EduMarkdownReferenceContributor"/>
  </extensions>
</idea-plugin>