Explain how encoding/json marshaling works with struct tags and custom marshalers.
encoding/json uses struct tags to control JSON field names and behavior. Implement json.Marshaler and json.Unmarshaler interfaces for custom serialization logic.
Struct tags and custom marshalers
Common pitfalls
Unexported fields are silently ignored — always export fields you want serialized
interface{} numbers unmarshal as float64 by default — use UseNumber() for large integers
omitempty omits zero values: 0, false, "", nil — careful with intentional zero values
Anonymous embedded structs promote their fields to the parent — useful but can cause field collisions
json.RawMessage allows deferring or passing through raw JSON without parsing