// -----------/
    // - Methods -/
    // -----------/

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

    /**
     * Method getExtensions.
     *
     * @return List
     */

        ClassExtensionMetaData extensionMetaData = new ClassExtensionMetaData('org.gradle.Class')
        extensionMetaData.addExtension('a', 'n1', 'org.gradle.ExtensionA1')
        extensionMetaData.addExtension('a', 'n2', 'org.gradle.ExtensionA2')
        extensionMetaData.addExtension('b', 'n1', 'org.gradle.ExtensionB')
        ClassDoc extensionA1 = classDoc('org.gradle.ExtensionA1')

        this.targetClass = targetClass
    }

    def void addMixin(String plugin, String mixinClass) {
        mixinClasses.add(new MixinMetaData(plugin, mixinClass))
    }

    def void addExtension(String plugin, String extension, String extensionClass) {
        extensionClasses.add(new ExtensionMetaData(plugin, extension, extensionClass))
    }

        Build build = project.getModel().getBuild();

        Extension extension = createExtension("other.group", "other-artifact", "1.0");

        build.addExtension(extension);

        new ProjectSorter(Collections.singletonList(project));
    }

    @Test
    void testMatchingArtifactIdsDifferentGroupIds() throws Exception {

                    if (!extensionId) {
                        throw new RuntimeException("No id specified for extension '$extensionClass' for plugin '$pluginId'.")
                    }
                    extension.addExtension(pluginId, extensionId, extensionClass)
                }
            }
        }
        return extensions
    }

    def mergeContent(Element typeTable, DslDocModel model) {