    # File lib/rmail/mailbox/mboxreader.rb, line 88
          def read_chunk(size)
            chunk = read_chunk_low(size)
            if chunk
              if chunk.length > @sep.length
                @tail = chunk[-@sep.length .. -1]
              else
                @tail ||= ''
                @tail << chunk
              end
            elsif @tail
              if @tail[-@sep.length .. -1] != @sep
                chunk = @sep
              end
              @tail = nil
            end
            chunk
          end