<DataSource ID="MockupContainer" inheritsFrom="Canvas" Constructor="MockupContainer">
    <!-- Note: propertiesOnly is required to avoid generating JS with nested create() calls -->
    <field name="dataSources" type="DataSource" multiple="true" propertiesOnly="true"/>
    <field name="components"  type="Canvas"     multiple="true" propertiesOnly="true"/>
</DataSource>
