sourceFilters()

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

Function in the Generator class: enables perl sources (should be valid for most generators).

Intention for subclasses: add own source filters.

Parameters: the object.

Return values: a filter list.

Hints: in most cases it will be useful to invoke the parent method, except when perl filters are not required, as by

    (
     $me->SUPER::sourceFilters,  # parent class list
     "xml",                      # embedded XML;
    );