Using foreign definitions

Sometimes definitions made by another module become important to a converter author, for example if a generalized version of existing tags becomes available.

    pp2html introduced various reference tags. After a
    while, it was decided to make a generalized reference
    tag \REF available with PerlPoint::Package.

To avoid multiple similar implementations, and to allow it to keep well known tag interfaces alive while using new features, or simply to use a tag from another definition module as base of an own tag definition, it is possible to call a foreign hook function from a tag hook, passing the tag name, the hook type ( hook or finish) and the usual parameters.

     $rc=PerlPoint::Tags::call('TAG', 'hook', @_);

If the tag is not registered, or has no hook of the specified type, an undefined value is supplied, otherwise you receive the return code of the invoked function.

By using this feature, one could translate own options to the options of the used "base" tag, invoke its hook, translate the values back and continue processing. The invoked hook might perform all one needs, or one might add own operations. One could even try to combine several other tags ...

Of course, for reasons of performance, it is not recommended to use this interface between tags declared in the same module. Please stay with usual function calls then to avoid an additional function call layer.