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checkUsage()

Invocation: called after the constructor of a subclass and options(), by the bootstrap() method.

Function in the Generator class: none that far.

Intention for subclasses: check usage, e.g. options.

Parameters: the object. Note that the option list is available in attribute options.

Return values: none expected. The method should terminate the program if necessary.

Hints: it is strongly recommended to invoke the parent method, as by

    # don't forget the base class
    $me->SUPER::checkUsage;