Restrict zone by level

[Baruuk]

Hi guys - I did a bit of searching on this and found similar things, but nothing that really answered the question I'm afraid.

What would you say is the easiest way to restrict all PoKnowledge teleport books so that you have to be lvl 20 or higher to use them? I'm willing to modify them one by one, but just not sure how to. The server idea I'm working with is to start in normal home cities and encourage exploration of the world (with some assistance) from lvls 1-20. Once you reach lvl 20, as a reward, you will be able to use the books to gain access to PoK. On a similar note, I'll have to figure out how to restrict access to PoK via running from Shar'Vhal, Paludal, etc. I would imagine it's similar, but related to a zone line? Any input is greatly appreciated.

Thanks gents.

Baruuk