What makes a pcp a pcp?

I've looked through various things in the act but I'll have a deeper look.

A rifle may be made a pcp, that still doesn't explain the definition.
No one seems to be able to say this is the written definition by nz law of a pcp. ( Im starting to wonder if there is one)
And if you can, point me to it please.
So let's skip CO2.
What about a different gas.
Nitrogen can be filled up to 6000 psi; air is typically not filled that high.
Its also used a propellent in gas powered rifles. Though I imagine not at that pressure as it would require a much stronger bottle. Different connections.
Arnt gas ram air rifles nitrogen filled?
The three things I see that may define a pcp are ability to fire multiple shots from one fill (as mentioned earlier in thread to me)
External Valves for filling from a outside source.
Semi auto which was a concern at the time.
Two of those can be found in lower powered CO2 guns.
The other is not viable as pcp pistols use them.
Here's some thing to think about, if there is no legal definition of a pcp, at some stage one will be written and in that definition will come a whole host of cross overs to other air guns.
Or maybe they bring in the 12fps across the board.
That will mean a lot of air rifles in ppls hands that will need a fal.

Can't a pcp be filled with CO2 to the higher pressure if required?
Would that then not be a pcp?

From what I can work out from what I can find, there is no definition. Technically its an air rifle and the only reason it has a special category, is it was issued one by Judith.
After the shootings the biggest issue was it was semi auto, so delived multiple shots to cop who died.
That would stand to reason as to why multi shot springers arnt banned, but not why CO2 arnt.

I’d look at it as prechargining with air for multiple shots.. co2 isn’t air so not pcp, multi pump charges for a single shot where the stored air is then expelled, so not pcp.
If there was a multipump that allowed stored air for more than one full power shot then I’d say it’s a pcp. There are pcps that have an integral pump for charging.