sort_repeated_fields_by_subfield.OUT.textproto

# txtpbfmt: sort_repeated_fields_by_subfield=oper.id
head {
  oper {
    id: "c"
    value: 42
  }
  oper {
    id: "m"
    value: 12
  }
  oper {
    id: "x"
    value: 29
  }
}