Application Note: Field Presence

Background Field presence is the notion of whether a protobuf field has a value. There are two different manifestations of presence for protobufs: implicit presence, where the generated message API stores field values (only), and explicit presence, where the API also stores whether or not a field has been set. Note We recommend always adding the optional label for proto3 basic types. This provides a smoother path to editions, which uses explicit presence by default.