"""
        file("a/build.gradle") << """
            plugins.apply(my.MyPlugin)
            myExtension.message = "the message"
        """
        file("b/build.gradle") << """
            plugins.apply(my.MyPlugin)
            def otherProject = project(':a')
            myExtension.message = otherProject.myExtension.message
        """

        when:
        executer.withArguments(ENABLE_CLI, WARN_PROBLEMS_CLI_OPT)

            $builderContent
            def message = project.myExtension.message.get()
            return new MyModel(message)
        """)

        addBuilderRegisteringPluginImplementation(childBuildName, "MyModelBuilder", """
            def model = project.extensions.create("myExtension", MyExtension)
            model.message = "It works from project \${project.identityPath}"
        """)
    }

        then:
        model2.size() == 2
        fixture.assertStateLoaded()
        outputDoesNotContain("Callback before")


        when:
        buildFile << """
            myExtension.message = "updated message for root"
        """

        withIsolatedProjects()
        def model3 = runBuildAction(new FetchCustomModelForEachProject())

        then:
        model3.size() == 2

        """

        file("b/build.gradle") << """
            import ${Property.name}

            interface MyExtension {
                Property<String> getFoo()
            }

            def myExtension = extensions.create('myExtension', MyExtension)
            myExtension.foo.set('configured')
        """

        when:

        buildFile << """
            abstract class MyExtension {
                abstract Property<String> getOther()

                Provider<String> getFoo() {
                    return other
                }
            }

            extensions.create("myext", MyExtension)
            myext {
                conventionMapping.map("foo", { project.provider { "foobar" } })

        and:
        fixture.assertStateLoaded()

        when:
        file("a/build.gradle") << """
            myExtension.message = 'this is project a'
        """
        file("b/build.gradle") << """
            myExtension.message = 'this is project b'
        """

        server.expect("configure-root")
        server.expectConcurrent("configure-a", "configure-b")

        model2[1].message == "It works from project :a"

        and:
        fixture.assertStateLoaded()
        outputDoesNotContain("creating model")

        when:
        buildFile << """
            myExtension.message = 'this is the root project'
        """

        executer.withArguments(ENABLE_CLI)
        def model3 = runBuildAction(new FetchCustomModelForEachProject())

        then:
        model3.size() == 2

        model2.message == "It works from project :"

        and:
        fixture.assertStateLoaded()
        outputDoesNotContain("creating model")

        when:
        buildFile << """
            myExtension.message = 'this is the root project'
        """

        executer.withArguments(ENABLE_CLI)
        def model3 = fetchModel()

        then:
        model3.message == "this is the root project"

include::sample[dir="snippets/plugins/mappingExtensions/groovy",files="app/build.gradle[tags=snippet]"]
====

In this example, the `MyExtension` class defines an `inputParameter` property that can be set in the build script.
The `MyPlugin` class configures this extension and uses its `inputParameter` value to configure the `MyCustomTask` task.