The primary subtype of text is "plain". This indicates plain (unformatted) text. The default Content-Type for Internet mail, "text/plain; charset=us-ascii", describes existing Internet practice. That is, it is the type of body defined by RFC 822.
No other text subtype is defined by this document.
The formal grammar for the content-type header field for text is as follows:
text-type := "text" "/" text-subtype [";" "charset" "=" charset] text-subtype := "plain" / extension-token charset := "us-ascii"/ "iso-8859-1"/ "iso-8859-2"/ "iso-8859-3" / "iso-8859-4"/ "iso-8859-5"/ "iso-8859-6"/ "iso-8859-7" / "iso-8859-8" / "iso-8859-9" / extension-token ; case insensitive