get Atom Property
Look up a property of this atom. Normal atoms have properties that can be set and read in this way, but specifically not enumerated by Avail code. You can see anything that you know how to look for, but everything else is thereby encapsulated.
Return
The value associated with that property key within the receiver, or nil if there is no such property in this atom.
Parameters
key
The property key to look up, an atom.