docs: Clarify semantics of multiple oneof variants passed to msg ctor (#263)
docs: Clarify semantics of multiple oneof variants passed to msg ctor (#263)

Example:

import proto

class Song(proto.Message):
    name = proto.Field(proto.STRING, number=1, oneof="identifier")
    database_id = proto.Field(proto.STRING, number=2, oneof="identifier")

s = Song(name="Canon in D minor", database_id="b5a37aad3")
assert "database_id" in s and "name" not in s

s = Song(database_id="e6aa708c7e", name="Little Fugue")
googleapis/proto-plus-python