Defines an area in the wireframe grid that serves as a placeholder for the content of child wireframes. This component must be added to wireframes representing pages that utilize content inheritance for their sub-pages. The wireframe of any child document that inherits the content will only be customizable inside this area, the remaining components will be displayed as fixed content.
Help URL: http://devnet.kentico.com/docs/webparts/index.html?Wireframe.NextPageLevel_overview.htm