public class ExtensionDescriptor {

    private List<String> exportedPackages;

    private List<String> exportedArtifacts;

    ExtensionDescriptor() {
        // hide constructor
    }

    public List<String> getExportedPackages() {
        if (exportedPackages == null) {
            exportedPackages = new ArrayList<>();
        }

        return exportedPackages;
    }

            for (CoreExtensionEntry entry : reversed) {
                Set<String> exportedPackages = entry.getExportedPackages();
                ClassRealm realm = entry.getClassRealm();
                for (String exportedPackage : exportedPackages) {
                    extRealm.importFrom(realm, exportedPackage);
                }
                if (exportedPackages.isEmpty()) {

    }

    public CoreExports(ClassRealm realm, Set<String> exportedArtifacts, Set<String> exportedPackages) {
        this.artifacts = Collections.unmodifiableSet(new HashSet<>(exportedArtifacts));
        this.packages = exportedPackages.stream()
                .collect(collectingAndThen(toMap(identity(), v -> realm), Collections::unmodifiableMap));
    }

    /**

    void testCompleteDescriptor() throws Exception {
        String xml = "<?xml version='1.0' encoding='UTF-8'?>" + "<extension>" + "<exportedPackages>"
                + "<exportedPackage>a</exportedPackage>" + "<exportedPackage>b</exportedPackage>"
                + "<exportedPackage>c</exportedPackage>" + "</exportedPackages>" + "<exportedArtifacts>"
                + "<exportedArtifact>x</exportedArtifact>" + "<exportedArtifact>y</exportedArtifact>"

            }

            return new ProjectRealmCache.CacheRecord(null, null);
        }

        List<ClassRealm> extensionRealms = new ArrayList<>();

        Map<ClassRealm, List<String>> exportedPackages = new HashMap<>();

        Map<ClassRealm, List<String>> exportedArtifacts = new HashMap<>();

        List<Artifact> publicArtifacts = new ArrayList<>();

        for (Plugin plugin : extensionPlugins) {

        HashSet<String> exportedPackages = new HashSet<String>();
        exportedPackages.add("group1:artifact1");

        return new DefaultClassRealmManager(
                new DefaultCoreRealm(container),
                new ArrayList<ClassRealmManagerDelegate>(),
                new CoreExports(new ClassRealm(null, "test", null), new HashSet<String>(), exportedPackages));
    }

    <exportedPackage>org.apache.maven.exception</exportedPackage>
    <exportedPackage>org.apache.maven.execution</exportedPackage>
    <exportedPackage>org.apache.maven.execution.scope</exportedPackage>
    <exportedPackage>org.apache.maven.feature</exportedPackage>
    <exportedPackage>org.apache.maven.graph</exportedPackage>
    <exportedPackage>org.apache.maven.lifecycle</exportedPackage>
    <exportedPackage>org.apache.maven.model</exportedPackage>

      <name>ExtensionDescriptor</name>
      <version>1.0.0</version>
      <description><![CDATA[Root element of the <code>extension.xml</code> file.]]></description>
      <fields>
        <field>
          <name>exportedPackages</name>
          <version>1.0.0</version>
          <association>
            <type>String</type>
            <multiplicity>*</multiplicity>
          </association>

            throw new IOException("Unexpected root element \"" + dom.name() + "\", expected \"extension\"");
        }

        extensionDescriptor.setExportedPackages(parseStrings(dom.child("exportedPackages")));

        extensionDescriptor.setExportedArtifacts(parseStrings(dom.child("exportedArtifacts")));

        return extensionDescriptor;
    }

    private List<String> parseStrings(XmlNode dom) {

                Set<String> exportedPackages = entry.getExportedPackages();
                ClassRealm realm = entry.getClassRealm();
                for (String exportedPackage : exportedPackages) {
                    extRealm.importFrom(realm, exportedPackage);
                }
                if (exportedPackages.isEmpty()) {