Whether an object of this class can have its #GESAsset change over its lifetime. This should be set to %TRUE if one of the object's parameters that is associated with its ID can change after construction, which would require an asset with a new ID. Note that the subclass is required to handle the requesting and setting of the new asset on the object.
The method to call to check whether a given ID is valid as an asset #GESAsset:id for the given #GESAsset:extractable-type. The returned ID is the actual #GESAsset:id that is set on the asset. The default implementation will simply always return the type name of the #GESAsset:extractable-type, even if the received ID is %NULL. As such, any given ID is considered valid (or is ignored), but only one is actually ever set on an asset, which means the given #GESAsset:extractable-type can only have one associated asset.
The subclass type of #GESAsset that should be created when an asset with the corresponding #GESAsset:extractable-type is requested.