Mapping rules file for nested custom messages

[shannenlolol]

Hi, I would like to ask how should a mapping rules file be for a nested custom message.

For example, I have a SystemStatus message that contains a BatteryStatus message:

SystemStatus:
BatteryStatus batterystatus
bool manualmode
bool remotenosignal

BatteryStatus:
float32 voltage
float32 current
float32 capacity
bool incharge

How should I write fileds_1_to_2? Thank you!