Proto3 defines typed messages and stable field numbers for shared payloads
Google’s proto3 language guide on .proto syntax, message fields, types, and generating data access classes.
The proto3 Language Guide explains how to structure protocol buffer data with .proto syntax and how generated access classes are produced. A message declares named, typed fields each assigned a field number. The edition or syntax line must be first; if omitted, the compiler assumes proto2.
Based on: Language Guide (proto 3) · Google