The task of type handlers is to resolve element specifications typically
taken from the command line arguments to a sequenece of objects that are
the processed to processing steps in a processing chain.
As such they work as data source for processing chains.
The are controlled by a generic function familiy HandleOutput(s) that handle
the API calls for the typoe handlers according to the actual set of
element specifications.
There are two basic methods:
All() - Without an element spec all possible elements are returned
Get() - If specs are given for every spec the Get method is called
to reolve the spec to a list of elements.