The command subsystem is reponsible for the user interaction
via the command line.
In addition, so-called global parameters
allow to keep and exchange numerical as well as character
data between user programs and the "outside world".
FAQ: How to ...
FAQ: Trouble shooting
Some import/export "filters" are implemented
on the command subsystem level because it is
the highest common level for a variety of home-grown packages.
Here is a collection of file format descriptions: