code: func (b *limitedBroadcast) Less(than btree.Item) bool {
  	o := than.(*limitedBroadcast)
  	if b.transmits < o.transmits {
  		return true
  	} else if b.transmits > o.transmits {
  		return false
  	}
  	if b.msgLen > o.msgLen {
  		return true
  	} else if b.msgLen < o.msgLen {
  		return false
  	}
  	return b.id > o.id
  }
docs: // Less tests whether the current item is less than the given argument.
  //
  // This must provide a strict weak ordering.
  // If !a.Less(b) && !b.Less(a), we treat this to mean a == b (i.e. we can only
  // hold one of either a or b in the tree).
  //
  // default ordering is
  // - [transmits=0, ..., transmits=inf]
  // - [transmits=0:len=999, ..., transmits=0:len=2, ...]
  // - [transmits=0:len=999,id=999, ..., transmits=0:len=999:id=1, ...]