DELETE MODEL deletes the current model object AND all associated objects, if any.  

The current model object is the one highlighted on the workmap and checkmarked in the model menu. 

Associated objects are:
1) All those "below" the current model object.  An object is "below" the current model object if a path of connecting lines exists from the lower edge of the current model object to the "below" object. A "below" object may be a data object, model object, or analysis object.
2) Those "emmediately above" the current model object. An object is "emmediately above"  the current model object if it is an analysis object which is connected directly to the upper edge of the model object. An "above" object may only be an analysis object.
