# File lib/soap/mimemessage.rb, line 50
    def parse(str)
      header_cache = nil
      str.each do |line|
        case line
        when /^\A[^\: \t]+:\s*.+$/
          parse_line(header_cache) if header_cache
          header_cache = line.sub(/\r?\n\z/, '')
        when /^\A\s+(.*)$/
          # a continuous line at the beginning line crashes here.
          header_cache << line
        else
          raise RuntimeError.new("unexpected header: #{line.inspect}")
        end
      end
      parse_line(header_cache) if header_cache
      self
    end