rfc2822 April 2001

1.3. Structure of this document

   This document is divided into several sections.

   This section, section 1, is a short introduction to the document.

   Section 2 lays out the general description of a message and its
   constituent parts.  This is an overview to help the reader understand
   some of the general principles used in the later portions of this
   document.  Any examples in this section MUST NOT be taken as
   specification of the formal syntax of any part of a message.

   Section 3 specifies formal ABNF rules for the structure of each part
   of a message (the syntax) and describes the relationship between
   those parts and their meaning in the context of a message (the
   semantics).  That is, it describes the actual rules for the structure
   of each part of a message (the syntax) as well as a description of
   the parts and instructions on how they ought to be interpreted (the
   semantics).  This includes analysis of the syntax and semantics of
   subparts of messages that have specific structure.  The syntax
   included in section 3 represents messages as they MUST be created.
   There are also notes in section 3 to indicate if any of the options
   specified in the syntax SHOULD be used over any of the others.

   Both sections 2 and 3 describe messages that are legal to generate
   for purposes of this standard.

   Section 4 of this document specifies an "obsolete" syntax.  There are
   references in section 3 to these obsolete syntactic elements.  The
   rules of the obsolete syntax are elements that have appeared in
   earlier revisions of this standard or have previously been widely
   used in Internet messages.  As such, these elements MUST be
   interpreted by parsers of messages in order to be conformant to this
   standard.  However, since items in this syntax have been determined
   to be non-interoperable or to cause significant problems for
   recipients of messages, they MUST NOT be generated by creators of
   conformant messages.

   Section 5 details security considerations to take into account when
   implementing this standard.

   Section 6 is a bibliography of references in this document.

   Section 7 contains the editor's address.

   Section 8 contains acknowledgements.

   Appendix A lists examples of different sorts of messages.  These
   examples are not exhaustive of the types of messages that appear on
   the Internet, but give a broad overview of certain syntactic forms.

   Appendix B lists the differences between this standard and earlier
   standards for Internet messages.

   Appendix C has copyright and intellectual property notices.