Hi vsespb, thanks for the clarification.

in my xml, my idea was that normal users will just change the flow if required. expert users will have additional feature to add pretasks/post tasks.

Idea is to identify a solution which supports plug and play/customization and at the same time provides flexibility to the flow. perl/xml solution is just an idea, we can ignore it if we have better solutions available.

Btw, updated question with a real life example.