That makes things much clearer for me, mr_mischief. Thanks so much for closing this gap in my understanding.

As for libraries, I have to admit I am not completely familiar with the concept. My understanding is that they are units of code with well defined interfaces that perform certain complex actions. Is it helpful to think of them as Perl objects which get created by my Perl programme via suitable constructors and subsequently addressed via appropriate methods or subroutines? Or are they actual programmes started by my Perl programme that run in parallel to it and then interact with it at runtime?

Thanks again in advance for clarifying.

Pat