The <regionBase> element groups a set of <region> elements, each of which may contain another set of nested <region> elements, and so on, recursively.

Each <regionBase> element is associated with a class of devices where presentation will take place. To identify the association, the <regionBase> element defines the device attribute. When the attribute is not specified, the presentation takes place in the same device that runs the NCL player.

There are two different types of device classes: active and passive. In an active class, a device is able to run some media players for <media> element presentations. In a passive class, a device is not required to run media players, only to exhibit a bit map or a sequence of audio samples received from another device.

The “deviceClass” property of a <media> element is initialized with the device value, if the <media> element indirectly refers to a <region> element inside a <regionBase>, by using a <descriptor> element.

The chosen class also defines the global environment variables (properties of the settings object —<media> element of “application/x-ncl-settings” type): “system.screenSize(i)”, “system.screenGraphicSize(i)”, and “system.audioType(i)”.

The “systemScreen(1)” and “systemAudio(1)” are reserved to passive classes, and “systemScreen(2)” and “systemAudio(2)” are reserved to active classes.

The <regionBase> element that defines a passive class may also have a region attribute. This attribute is used to identify a <region> element in another <regionBase> associated with the parent device that creates the bit map sent to the passive class; in the specified region the bit map must also be exhibited. The “system.parentDeviceRegion(i)” property of the settings object (<media> element of “application/x-ncl-settings” type) is initialized with the region attribute value.