container objects

Containers are objects that hold other objects (sometimes I called them
meta-objects, since one hardly uses them directly) get all of the methods of
[standard objects], plus 2 to 4 additional methods:

• the index operator[],
• or containment test (in)

The getstate method returns the size of the container or the number of other
elements within it.

This is a preliminary exploration. It may be that more methods will be
necessary, like size or a test for non-zero, yet I believe these can be
accommodated with get_state.... [STUB]

A built-in Stack object exists in the shell offering a First-In, Last-Out
container. The shell stack can be accessed with what operator, symbol, or
name?

The Stack(Container) adds push, pop