provides context information for an ECHO processor
ECHOContext objects provide the ECHO processor the ability
to pass parameters to nested ECHO request handlers
ECHOContext objects may contain a handle to a "parent"
context.
returns only a smaller window of a flattish XML structure, using
the context parameters "skip" for the number of initial elements at
a given depth in the tree to ignore, "count" the number of elements
to return, and "depth" to indicate at what depth in the XML tree
the other two parameters operate