Guidelines for Attachments

Submissions to W3C mailing lists are intended to be viewed by a broad audience of current and future viewers. Although email messages themselves are normally sent in plain text or HTML format, attachments in other formats are sometimes included. Learn more about:


Many people have expressed concern about formats that are sometimes used in email attachments that are submitted to W3C mailing lists. These concerns include:

  • Fear of potential virus transmission
  • Inability to read the format, because the recipient is running on a different platform than the sender and does not have the necessary viewing software
  • Difficulty reading the format because it requires a specialized viewer that must be separately purchased or installed
  • Difficulty using the format in conjunction with HTML (for example, difficulty in extracting an excerpt for use in an HTML document)
  • Reservations about using formats whose specifications are proprietary, unpublished or not freely implementable.


In discussing these concerns, several observations were made:

  • Many documents that are submitted in a format that raises these concerns could have been submitted in a different format that does not raise these concerns, without substantial loss in value to the reader.
  • Mailing list submissions are permanently archived and may be need to be searched and read by many people for years to come.
  • A submitted document has only one sender, but could potentially have hundreds or thousands of readers; therefore
  • It seems far more reasonable to place any format conversion burden on the sender of a document than on its (potentially many) readers.

As a result of these concerns, we have adopted several guidelines.


Submissions to W3C email lists should conform to the following guidelines.

  1. Avoid unnecessary email attachments.  Use an attachment only when it is likely to benefit to recipients. Otherwise, place the information (in plain text format) in the body of your message.
  2. If an attachment is necessary, avoid formats that are virus prone, proprietary or platform dependent.  For example, whenever possible you should use HTML instead of MS Word, PowerPoint or PDF.  (Ideally, use XHTML or HTML4.)  
  3. If you must use a proprietary or platform-dependent format, please also include an alternate version in  a universally readable format, such as HTML or plain text, if possible. If you cannot, then at least include a format that has widely available free viewers, if possible.
  4. Beware of automatic conversions to HTML.  They often produce HTML that can only be viewed on certain browsers.  HTML Tidy may be helpful in cleaning up HTML.
  5. Avoid JavaScript and proprietary extensions in HTML.
  6. Follow Web Content Accessibility Guidelines (WCAG).