serializer.setPrefix("", "http://maven.apache.org/EXTENSIONS/1.1.0");
        serializer.setPrefix("xsi", "http://www.w3.org/2001/XMLSchema-instance");
        serializer.startTag(NAMESPACE, tagName);
        serializer.attribute(
                "",
                "xsi:schemaLocation",
                "http://maven.apache.org/EXTENSIONS/1.1.0 https://maven.apache.org/xsd/core-extensions-1.1.0.xsd");

                extensions.add(createExtension(extension, artifacts));
            }
        }

        return Collections.unmodifiableList(extensions);
    }

    private CoreExtensionEntry createExtension(CoreExtension extension, List<Artifact> artifacts) throws Exception {
        String realmId = "coreExtension>" + extension.getGroupId() + ":" + extension.getArtifactId() + ":"
                + extension.getVersion();

  <name>Maven Integration Test :: MNG-3899</name>
  <description>
    Test that build extensions are properly merged during inheritance.
  </description>

  <build>
    <extensions>
      <extension>
        <groupId>org.apache.maven.its.mng3899</groupId>
        <artifactId>a</artifactId>
        <version>0.1</version>
      </extension>
      <extension>
        <groupId>org.apache.maven.its.mng3899</groupId>

    }

    /**
     * Returns artifacts exported by Maven core and core extensions. Artifacts are identified by their
     * groupId:artifactId string key.
     */
    public Set<String> getExportedArtifacts() {
        return artifacts;
    }

    /**
     * Returns packages exported by Maven core and core extensions.
     */
    public Map<String, ClassLoader> getExportedPackages() {
        return packages;

import org.apache.maven.execution.MavenSession;

/**
 * Allows core extensions to participate in Maven build session lifecycle.
 *
 * All callback methods (will) follow beforeXXX/afterXXX naming pattern to
 * indicate at what lifecycle point it is being called.
 *
 * @see <a href="https://maven.apache.org/examples/maven-3-lifecycle-extensions.html">example</a>
 * @see <a href="https://issues.apache.org/jira/browse/MNG-4224">MNG-4224</a>

 *   <li>{@link org.apache.maven.api.cli.Options} - Represents Maven configuration options</li>
 *   <li>{@link org.apache.maven.api.cli.extensions.CoreExtensions} - Manages Maven core extensions</li>
 * </ul>
 *
 * <p>Core extensions can be configured through {@code .mvn/extensions.xml} in the project base directory
 * to enhance Maven's capabilities during build execution.</p>
 *
 * @since 4.0.0
 */

 */

/**
 * Provides support for Maven core extensions configuration and management.
 *
 * <p>This package contains classes for:</p>
 * <ul>
 *   <li>Extension configuration model</li>
 *   <li>Extension loading and validation</li>
 *   <li>Extension lifecycle management</li>
 * </ul>
 *
 * @since 4.0.0
 */

        if (build != null) {
            for (Extension extension : build.getExtensions()) {
                Plugin plugin = new Plugin();
                plugin.setGroupId(extension.getGroupId());
                plugin.setArtifactId(extension.getArtifactId());
                plugin.setVersion(extension.getVersion());
                XmlNode configuration = extension.getDelegate().getConfiguration();

Use this directory to add third party extensions to Maven Core. These extensions can either extend or override

   * <<<{{{./apidocs/org/apache/maven/api/cli/mvnup/package-summary.html}mvnup}}>>>, the Maven Upgrade tool.

 This API also defines {{{./core-extensions.html}Core Extensions model}} for <<<.mvn/extensions.xml>>>.