Sometimes, an input-file is read and modified, but should not be written
back to disk. However, writing a file back is an almost instinctive action
when terminating your editing-session. Even worse, many people have macros
in place which automatically write on exit.

The protect register is not very useful in this case, because
it does the opposite. It does not allow a register to be modified!

A very convenient, quick and 100% safe method is, to change the default
file name for the buffer directly after reading the file:

   Y holy_file ESC ;Y NIL: ESC ESC        (Amiga)
   Y holy_file ESC ;Y /dev/null ESC ESC   (Unix)
   Y holy_file ESC ;Y NIL ESC ESC         (Windows)

If the file is now written, it is written to the nil-device instead of
on top of the sacred file.