    # File lib/action_mailer/vendor/tmail-1.2.3/tmail/quoting.rb, line 61
          def unquote_and_convert_to(text, to_charset, from_charset = "iso-8859-1", preserve_underscores=false)
            return "" if text.nil?
            text.gsub(/(.*?)(?:(?:=\?(.*?)\?(.)\?(.*?)\?=)|$)/) do
              before = $1
              from_charset = $2
              quoting_method = $3
              text = $4

              before = convert_to(before, to_charset, from_charset) if before.length > 0
              before + case quoting_method
                  when "q", "Q" then
                    unquote_quoted_printable_and_convert_to(text, to_charset, from_charset, preserve_underscores)
                  when "b", "B" then
                    unquote_base64_and_convert_to(text, to_charset, from_charset)
                  when nil then
                    # will be nil at the end of the string, due to the nature of
                    # the regex used.
                    ""
                  else
                    raise "unknown quoting method #{quoting_method.inspect}"
                end
            end
          end