@node Usage rules
+@cindex usage rules
@unnumbered Usage rules
@itemize
@code{$3} file. You have to produce either @code{stdout} output, or
use @code{$3} directly, but not both.
-@item If there was no @code{stdout} output and no @code{$3} file is
- explicitly created, then no output file is created at all. Target
- does not produce anything, it is "empty".
+@item If neither @code{stdout} output nor @code{$3} file were
+ explicitly created, then no output file is created at all.
+ Target does not produce anything, it is "non-existent".
@item @code{stderr} is not captured at all and can be seen by default.
-@item Empty targets are considered always out-of-date.
+@item Non-existent targets are considered always out-of-date.
@item Dependency information is recorded by @command{redo-ifchange}
command invocation. It takes list of dependencies (targets), on