code: def filename?(part)
        name = part.filename
        if (name.nil? || name.empty?)
          if part.content_id && (matched = /^<(.+)>$/.match(part.content_id))
            name = matched[1]
          else
            name = "#{Time.now.to_f}.#{self.default_ext(part.part_type?)}"
          end
        end
        # FIXME FWIW, janky look for dot extension 1 to 4 chars long
        name = (name =~ /\..{1,4}$/ ? name : "#{name}.#{self.default_ext(part.part_type?)}").strip
  
        # handle excessively large filenames
        if name.size > 255
          ext = File.extname(name)
          base = File.basename(name, ext)
          name = "#{base[0, 255 - ext.size]}#{ext}"
        end
  
        name
      end
docs: returns a filename declared for a part, or a default if its not defined