GROUP command
The GROUP command is a pseudo command used to provide flow control between
many other queue commands. The GROUP command is the beginning of a group of queue commands.
Each GROUP command has a multiprocessing option with the same meaning as the
the EXEC command. The GROUP command is thread-based on the name assigned the
GROUP in the first line. The first line also defines the expiration time of the
GROUP of commands. Each subsequent line in the GROUP defines a command to be run and
the flow control options are for that command. There is a set of options for when
the current command completes successfully and another set of options for when it
fails. The options include, how many times to execute the current command, and what
command to do next. The end of the GROUP is signalled with an ENDGROUP flag.