# File lib/rmail/parser/pushbackreader.rb, line 140
      def self.maybe_contains_re(boundary)
        left = Regexp.quote(boundary[0,1])
        right = ''
        boundary[1..-1].each_byte { |ch|
          left << '(?:'
          left << Regexp.quote(ch.chr)
          right << '|\z)'
        }
        left + right
      end