transform!

# File actionmailer/lib/action_mailer/inline_preview_interceptor.rb, line 30
    def transform! # :nodoc:
      return message if html_part.blank?

      html_part.body = html_part.decoded.gsub(PATTERN) do |match|
        if part = find_part(match[9..-2])
          %[src="#{data_url(part)}"]
        else
          match
        end
      end

      message
    end