In addition to generic error messages, jam may emit one of the following:
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 warning: unknown rule X    A rule was invoked that has not been defined with an "actions" or "rule" statement.
 using N temp target(s)    Targets marked as being temporary (but nonetheless present) have been found.
 updating N target(s)    Targets are out-of-date and will be updated.
 can't find N target(s)    Source files can't be found and there are no actions to create them.
 can't make N target(s)    Due to sources not being found, other targets cannot be made.
 warning: X depends on itself    A target depends on itself either directly or through its sources.
 don't know how to make X    A target is not present and no actions have been defined to create it.
 X skipped for lack of Y    A source failed to build, and thus a target cannot be built.
 warning: using independent target X    A target that is not a dependency of any other target is being referenced with \$(<) or \$(>).
 X removed    <b>Jam</b>  removed a  partially built target after being interrupted.
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