if (org != val) {
                    plugin.setVersion(val);
                }
                // Extensions
                org = plugin.getExtensions();
                val = interpolate(org);
                if (org != val) {
                    plugin.setExtensions(val);
                }
                // Executions
                for (PluginExecution execution : plugin.getExecutions()) {

        }
    }

    protected void mergeBuild_Extensions(
            Build target, Build source, boolean sourceDominant, Map<Object, Object> context) {
        target.setExtensions(
                merge(target.getExtensions(), source.getExtensions(), sourceDominant, new ExtensionKeyComputer()));
    }

    protected void mergeExtension(

                java.util.List<CoreExtension> extensions = coreExtensions.getExtensions();
                if (extensions == null) {
                    extensions = new java.util.ArrayList<CoreExtension>();
                }
                extensions.add(parseCoreExtension(parser, strict));
                coreExtensions.setExtensions(extensions);
            } else {
                checkUnknownElement(parser, strict);

                            List.copyOf(new CoreExtensionsStaxReader()
                                    .read(is, true, InputSource.of(extensionsFile.toString()))
                                    .getExtensions()),
                            allowMetaVersions);
                }
            }
            return List.of();
        } catch (XMLStreamException | IOException e) {

    }

    public List<Extension> getBuildExtensions() {
        Build build = getBuild();
        if ((build == null) || (build.getExtensions() == null)) {
            return Collections.emptyList();
        } else {
            return Collections.unmodifiableList(build.getExtensions());
        }
    }

    public void addProjectReference(MavenProject project) {
        projectReferences.put(

                            EMPTY,
                            problems,
                            errOn30,
                            Version.V20,
                            p.getExtensions(),
                            p.getKey(),
                            p);

                    validate20EffectivePluginDependencies(problems, p, request);
                }

            // extensionArtifacts
            Set<Artifact> extensionArtifacts = new HashSet<>();
            List<Extension> extensions =
                    project.getModel().getDelegate().getBuild().getExtensions();
            if (extensions != null) {
                for (Extension ext : extensions) {
                    String version;
                    if (ext.getVersion() == null || ext.getVersion().isEmpty()) {

    public boolean isExtensions() {
        return (getExtensions() != null) ? Boolean.parseBoolean(getExtensions()) : false;
    }
            ]]>
          </code>
        </codeSegment>
        <codeSegment>
          <version>4.0.0/4.0.99</version>
          <code>
            <![CDATA[
    public void setExtensions(boolean extensions) {
        setExtensions(String.valueOf(extensions));
    }

    /**

                    return new CoreExtensionsStaxReader()
                            .read(is, true, InputSource.of(extensionsFile))
                            .getExtensions();
                }
            }
        }
        return List.of();
    }

    private ClassRealm setupContainerRealm(

        assertEquals(3, artifacts.size()); // original jar + consumer pom + build pom

        assertTrue(artifacts.stream().anyMatch(a -> "pom".equals(a.getExtension()) && "".equals(a.getClassifier())));
        assertTrue(
                artifacts.stream().anyMatch(a -> "pom".equals(a.getExtension()) && "build".equals(a.getClassifier())));
    }

    @Test
    void testDeployBuildPomDisabled() {