The TMExceptionLeafTMNode exception is raised when
a TMNodeModelRoot received a TMEventUpdate event
for adding or removing a child to a TMNode that is a leaf.
The TMModelUpdater interface represents the object that
a TMModelNode should call to notify the treemap that something
has changed : size, state, numers of childs, ...
The TMUpdater interface represents the object that
a TMNode should call to notify the treemap that something
has changed : size, state, numers of childs, ...