date if it does not exist or if it is older than any of the dependencies
(by comparison of last-modification times). The idea is that the contents
of the target file are computed based on information in the dependencies,
-so if any of the dependencies changes the contents of the existing target
+so if any of the dependencies changes, the contents of the existing target
file are no longer necessarily valid.
How to update is specified by @var{commands}. These are lines to be