Macro entity_behaviour

macro_rules! entity_behaviour {
    (
        /// The ident of the behaviour.
        $behaviour: ident,
        /// The ident of the factory to create instances of the behaviour.
        $factory: ident,
        /// The ident of the finite state machine of the behaviour.
        $fsm: ident,
        /// The ident of the transitions of the finite state machine.
        $transitions: ident,
        /// The ident of the property validator of the behaviour.
        $validator: ty
        $(,
            // Function name.
            $fn_name: ident,
            // Function.
            $fn_ident: ident
        )*
        $(,)?
    ) => { ... };
}