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();

        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");

    }

    /**
     * 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;

maven.user.toolchains         = ${maven.user.conf}/toolchains.xml

#
# Extensions
#
maven.installation.extensions = ${maven.installation.conf}/extensions.xml
maven.project.extensions      = ${maven.project.conf}/extensions.xml
maven.user.extensions         = ${maven.user.conf}/extensions.xml

#
# Maven central repository URL.
#

  <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>

  <id>extension</id>
  <name>ExtensionDescriptor</name>
  <description><![CDATA[
    Extension descriptor, stored in <code>META-INF/maven/extension.xml</code> in an extension's jar artifact to
    precisely control parts of the extension and dependencies to expose in the API class loader.

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>

            gradleRootProject.extensions.extraProperties.set("collectedInfo-${klass.simpleName}-${rootProjectName}", buildService.get().collectedInformation)

            if (!isInBuildLogic) { // BuildScanExtension is only available in the gradle project
                val infoCollectedInBuildLogic = gradleRootProject.extensions.extraProperties.get("collectedInfo-${klass.simpleName}-build-logic")!!

 *   <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
 */

              return
            }

          // Apply the extensions. If they're unacceptable initiate a graceful shut down.
          // TODO(jwilson): Listeners should get onFailure() instead of onClosing() + onClosed(1010).
          val extensions = WebSocketExtensions.parse(response.headers)
          this@RealWebSocket.extensions = extensions
          if (!extensions.isValid()) {
            synchronized(this@RealWebSocket) {