# File lib/rmail/parser/pushbackreader.rb, line 35
      def initialize(input)
        unless defined? input.read(1)
          unless input.is_a?(String)
            raise ArgumentError, "input object not IO or String"
          end
          @pushback = input
          @input = nil
        else
          @pushback = nil
          @input = input
        end
        @chunk_size = 16384
      end