# File lib/bson/grow.rb, line 72
    def push!(bson) # Appends BSON element value with correct key unfinished
      @a_index ||= [0]
      @b_pos ||= [0]
      put_binary(bson.to_t)
      put_binary(@a_index[-1].to_s)
      put_binary(NULL_BYTE)
      @a_index[-1] += 1
      put_binary(bson.to_v)
      self
    end