mapping to be performed.  In particular, use of external profiling
   information to determine the exact mapping is not permitted.

   NOTE: The term "character set" was originally to describe such
   straightforward schemes as US-ASCII and ISO-8859-1 which have a
   simple one-to-one mapping from single octets to single characters.
   Multi-octet coded character sets and switching techniques make the
   situation more complex. For example, some communities use the term
   "character encoding" for what MIME calls a "character set", while
   using the phrase "coded character set" to denote an abstract mapping
   from integers (not octets) to characters.

2.3.  Message

   The term "message", when not further qualified, means either a
   (complete or "top-level") RFC 822 message being transferred on a
   network, or a message encapsulated in a body of type "message/rfc822"
   or "message/partial".

2.4.  Entity

   The term "entity", refers specifically to the MIME-defined header
   fields and contents of either a message or one of the parts in the
   body of a multipart entity.  The specification of such entities is
   the essence of MIME.  Since the contents of an entity are often
   called the "body", it makes sense to speak about the body of an
   entity.  Any sort of field may be present in the header of an entity,
   but only those fields whose names begin with "content-" actually have
   any MIME-related meaning.  Note that this does NOT imply thay they
   have no meaning at all -- an entity that is also a message has non-
   MIME header fields whose meanings are defined by RFC 822.







 
RFC 2045                Internet Message Bodies            November 1996


2.5.  Body Part

   The term "body part" refers to an entity inside of a multipart
   entity.

2.6.  Body

   The term "body", when not further qualified, means the body of an
   entity, that is, the body of either a message or of a body part.

   NOTE:  The previous four definitions are clearly circular.  This is
   unavoidable, since the overall structure of a MIME message is indeed
   recursive.

2.7.  7bit Data

   "7bit data" refers to data that is all represented as relatively
   short lines with 998 octets or less between CRLF line separation
   sequences [RFC-821].  No octets with decimal values greater than 127
   are allowed and neither are NULs (octets with decimal value 0).  CR
   (decimal value 13) and LF (decimal value 10) octets only occur as
   part of CRLF line separation sequences.

2.8.  8bit Data

   "8bit data" refers to data that is all represented as relatively
   short lines with 998 octets or less between CRLF line separation
   sequences [RFC-821]), but octets with decimal values greater than 127
   may be used.  As with "7bit data" CR and LF octets only occur as part
   of CRLF line separation sequences and no NULs are allowed.

2.9.  Binary Data

   "Binary data" refers to data where any sequence of octets whatsoever
   is allowed.

2.10.  Lines

   "Lines" are defined as sequences of octets separated by a CRLF
   sequences.  This is consistent with both RFC 821 and RFC 822.
   "Lines" only refers to a unit of data in a message, which may or may
   not correspond to something that is actually displayed by a user
   agent.









 
RFC 2045                Internet Message Bodies            November 1996


3.  MIME Header Fields