The Types module implements core object types, such as:
Address
Hash
Header
lots of helper functions
Unlike clients such as GETH, the ZChains doesn't use reflection for the encoding. The preference was to not use reflection because it introduces new problems, such as performance degradation, and harder scaling.
The Types module provides an easy-to-use interface for RLP marshaling and unmarshalling, using the FastRLP package.
Marshaling is done through the MarshalRLPWith and MarshalRLPTo methods. The analogous methods exist for unmarshalling.
By manually defining these methods, the ZChains doesn't need to use reflection. In rlp_marshal.go, you can find methods for marshaling:
Bodies
Blocks
Headers
Logs
Transactions