Dear Fadi,
in order to develop a concrete container class, that would support the automatic linking using the "Is inside" relation by the platform, please follow the steps below:
1) Inherit the container class from the "__D_aggregation__" if the functionality is supposed to work as modelling object, or u se "__D_swimlane__" for as swimlane behaviour. Both abstract classes are derived from the "__D_container__" class the provides the functionality of "Is inside" (see attached metamodel screenshot)
2) Include (as for all other classes) in the "Modi" for specific modeltypes you want to use the class. The functionality of "Is inside" is available in all functionalties of the platform (see example screenshots and files for the Analysis component and the XML export