Hello,
"maop" refers to the "Maximum allowable operating pressure" (https://en.wikipedia.org/wiki/Maximum_allowable_operating_pressure).
This is usually different from the actual average pressure, sometimes even extremely different. This has various reasons, common example are changing natural gas markets.

The normal "pressure" key dosen't make an obvious distinction between those two types of pressure, therefore I created this key.
I don't know if it's a good solution, maybe it's better to use only one key, maybe not. I don't have strong opinions on it.