!File: Pointing to Another File:
    So far we have been dealing with a two-level database consisting of
    short entries that expand to long entries. However, we can also have a
    short entry expand to another list of short entries. Unlike a long
    entry, which can be typed directly under its short entry, a list of
    short entries must be placed in a separate file. We can also place a
    single long entry in a file by itself and expand to it from a short
    entry. The !file: command allows us to accomplish both of these tasks.

    Example of expanding to another list of short entries from a short entry:

  +.!short Easy Listening by Category.                                  
 ++.!file: softrock.ngo                                                 
 ||
 |+-------  When ENTER is pressed, this short entry will.....
 |
 +--------  will display the short entries in the "softrock" file.


    Example of expanding to a single long entry contained in a separate file:

  +.!short List of CD's on loan.                                         
 ++.!file: cd_loan.ngo                                                  
 ||
 |+-------  When ENTER is pressed, this short entry will.....
 |
 +--------  will display the long detailed entry in the "cd_loan" file.

    This ends the tutorial session. Refer to the reference section for a
    more detailed look at each command and how it is implemented.