Usually an object that implements this interface
also implements XPropertySet and at
least some of the properties have subproperties.
This interface allows direct access to subsubproperties, ...
up to an arbitrary nesting depth. Often the intermediate
elements of the hierarchy implement XProperty.
Each implementation specifies how the
hierarchical property names, that are
used to access the elements of the hierarchy,
are formed.
Commonly a notation similar to filesystem pathes
(separated by '/' slashes) or nested module names
(separated by dots '.' or '::') is used.