code: function getItemPropertyKey(itemID, propName) {
  	if (itemID === undefined || propName === undefined) {
  		throw new Error("itemID and propName are required for keys.getItemPropertyKey")
  	}
  	return 'I' + itemID + '@' + propName
  }
docs: item properties are stored at 		I<item id>@<propName>	e.g. I20@books channel names for items are			#I<item id>				e.g. #I20 channel names for properties are		#P<propName>			e.g. #Pbooks Data state keys