Field	Type	Required	Description
name	string	+	An expression name. Should be unique across all the scenes.
code	string	+	Lua code snippet to be run within a scene (Max 5 kb for Linux and 1 kb for Atom)
params	object	–	Expression parameters
params.items	array of objects	–	An array of an expression parameter name and item identifier pairs.
params.items[index].name	string	+	A parameter name to use in an expression. A value of an item can be referred from an expression as params.name.
params.items[index]._id	string	+	An item identifier to get value from
params.device_item_names	array of objects	–	An array of an expression parameter name, device name and item item name objects.
params.device_item_names[index].name	string	+	A parameter name to use in an expression. A value of an item can be referred from an expression as params.name.
params.device_item_names[index].deviceName	string	+	A device name to get items from
params.device_item_names[index].itemName	string	+	An item name from the device pointed by deviceName, to use in an expression
valueType	string	–	A type of value returned by an expression. Required for expressions used by the Scenes Engine. If set, the Lua code should return only values, from which the variable of a given value type can be constructed. The valueType field can have any value the firmware exposes as an item value type.
metadata	object	–	Metadata bound to an expression. Can be JSON object type. If null, should not be stored.
variable	boolean	–	If true, the expression is a variable. Variables should be separated in the UI from other expressions. If a variable is true, the expression cannot get any data sources from outside (devices, items), and is supposed to save a constant never-changing value.
value	any type	–	Expression value