| 32 | bits | response tag |
| rest | return data (if any) |
The response tag can have the following values:
| TAG | MEANING |
| CONFIRM_REPLY | confirmation (for synchronization) |
| VALUES_REPLY | return values from a request |
| CALLBACK_REPLY | a widget callback has been invoked |
| EVENT_REPLY | an X event handler has been invoked |
| ERROR_REPLY | an error has occurred |
| WARNING_REPLY | a non-fatal problem has occurred |
| PROTOCOL_REPLY | a protocol callback has been invoked |