* @see Constants#MAVEN_INSTALLATION_EXTENSIONS
 */
@Experimental
public record CoreExtensions(Path source, List<CoreExtension> coreExtensions) {
    public CoreExtensions(Path source, List<CoreExtension> coreExtensions) {
        this.source = requireNonNull(source, "source");
        this.coreExtensions = requireNonNull(coreExtensions, "coreExtensions");
    }

    /**
     * Method addExtension.
     *
     * @param coreExtension a coreExtension object.
     */
    public void addExtension(CoreExtension coreExtension) {
        getExtensions().add(coreExtension);
    } // -- void addExtension( CoreExtension )

    /**
     * Method getExtensions.
     *
     * @return List
     */
    public List<CoreExtension> getExtensions() {
        if (this.extensions == null) {

        serializer.startDocument(coreExtensions.getModelEncoding(), null);
        writeCoreExtensions(coreExtensions, "extensions", serializer);
        serializer.endDocument();
    } // -- void write( Writer, CoreExtensions )

    /**
     * Method write.
     *
     * @param stream a stream object.
     * @param coreExtensions a coreExtensions object.
     * @throws IOException IOException if any.
     */

                String key = coreExtension.getGroupId() + ":" + coreExtension.getArtifactId();
                CoreExtension conflict = selectedExtensions.putIfAbsent(key, coreExtension);
                if (conflict != null && !Objects.equals(coreExtension.getVersion(), conflict.getVersion())) {
                    conflicts.add(String.format(

     * @throws XmlPullParserException XmlPullParserException if
     * any.
     * @return CoreExtensions
     */
    private CoreExtensions parseCoreExtensions(XmlPullParser parser, boolean strict)
            throws IOException, XmlPullParserException {
        String tagName = parser.getName();
        CoreExtensions coreExtensions = new CoreExtensions();
        for (int i = parser.getAttributeCount() - 1; i >= 0; i--) {

    }

    @Override
    public Optional<Path> rootDirectory() {
        return Optional.ofNullable(rootDirectory);
    }

    @Override
    public Optional<List<CoreExtensions>> coreExtensions() {
        return Optional.ofNullable(coreExtensions);
    }

    @Override
    public Optional<CIInfo> ciInfo() {
        return Optional.ofNullable(ciInfo);
    }

    public Optional<Options> options() {

        }
    }

    protected List<CoreExtension> validateCoreExtensionsDescriptorFromFile(
            Path extensionFile, List<CoreExtension> coreExtensions, boolean allowMetaVersions) {
        Map<String, List<InputLocation>> gasLocations = new HashMap<>();
        Map<String, List<InputLocation>> metaVersionLocations = new HashMap<>();
        for (CoreExtension coreExtension : coreExtensions) {

     * {@link CoreExtensions} is validated, but the list elements may have overlapping elements, that requires
     * some logic to sort out (like precedence).
     * <p>
     * The list of {@link CoreExtensions} if present, is in precedence order.
     *
     * @return an {@link Optional} containing the {@link CoreExtensions}, or empty if not configured
     */
    @Nonnull

          <version>1.0.0+</version>
          <association xml.itemsStyle="flat">
            <type>CoreExtension</type>
            <multiplicity>*</multiplicity>
          </association>
        </field>
      </fields>
    </class>
    <class xml.tagName="extension">
      <name>CoreExtension</name>
      <description>Describes a build extension to utilise.</description>
      <version>1.0.0+</version>

import java.util.List;

import org.apache.maven.api.annotations.Nonnull;
import org.apache.maven.api.cli.InvokerRequest;
import org.apache.maven.api.cli.extensions.CoreExtension;

/**
 * Core extension selector: selects which entries to load from {@link InvokerRequest#coreExtensions()}.
 *
 * @param <C> The context type.
 */
public interface CoreExtensionSelector<C extends LookupContext> {
    /**