📄 rfc2048.txt
字号:
created for external registration and management by well-known
permanent bodies, such as scientific societies for media types
specific to the sciences they cover. In general, the quality of
review of specifications for one of these additional registration
trees is expected to be equivalent to that which IETF would give to
registrations in its own tree. Establishment of these new trees will
be announced through RFC publication approved by the IESG.
2.2. Registration Requirements
Media type registration proposals are all expected to conform to
various requirements laid out in the following sections. Note that
requirement specifics sometimes vary depending on the registration
tree, again as detailed in the following sections.
2.2.1. Functionality Requirement
Media types must function as an actual media format: Registration of
things that are better thought of as a transfer encoding, as a
character set, or as a collection of separate entities of another
type, is not allowed. For example, although applications exist to
decode the base64 transfer encoding [RFC 2045], base64 cannot be
registered as a media type.
This requirement applies regardless of the registration tree
involved.
2.2.2. Naming Requirements
All registered media types must be assigned MIME type and subtype
names. The combination of these names then serves to uniquely
identify the media type and the format of the subtype name identifies
the registration tree.
The choice of top-level type name must take the nature of media type
involved into account. For example, media normally used for
representing still images should be a subtype of the image content
type, whereas media capable of representing audio information belongs
Freed, et. al. Best Current Practice [Page 6]
RFC 2048 MIME Registration Procedures November 1996
under the audio content type. See RFC 2046 for additional information
on the basic set of top-level types and their characteristics.
New subtypes of top-level types must conform to the restrictions of
the top-level type, if any. For example, all subtypes of the
multipart content type must use the same encapsulation syntax.
In some cases a new media type may not "fit" under any currently
defined top-level content type. Such cases are expected to be quite
rare. However, if such a case arises a new top-level type can be
defined to accommodate it. Such a definition must be done via
standards-track RFC; no other mechanism can be used to define
additional top-level content types.
These requirements apply regardless of the registration tree
involved.
2.2.3. Parameter Requirements
Media types may elect to use one or more MIME content type
parameters, or some parameters may be automatically made available to
the media type by virtue of being a subtype of a content type that
defines a set of parameters applicable to any of its subtypes. In
either case, the names, values, and meanings of any parameters must
be fully specified when a media type is registered in the IETF tree,
and should be specified as completely as possible when media types
are registered in the vendor or personal trees.
New parameters must not be defined as a way to introduce new
functionality in types registered in the IETF tree, although new
parameters may be added to convey additional information that does
not otherwise change existing functionality. An example of this
would be a "revision" parameter to indicate a revision level of an
external specification such as JPEG. Similar behavior is encouraged
for media types registered in the vendor or personal trees but is not
required.
2.2.4. Canonicalization and Format Requirements
All registered media types must employ a single, canonical data
format, regardless of registration tree.
A precise and openly available specification of the format of each
media type is required for all types registered in the IETF tree and
must at a minimum be referenced by, if it isn't actually included in,
the media type registration proposal itself.
Freed, et. al. Best Current Practice [Page 7]
RFC 2048 MIME Registration Procedures November 1996
The specifications of format and processing particulars may or may
not be publically available for media types registered in the vendor
tree, and such registration proposals are explicitly permitted to
include only a specification of which software and version produce or
process such media types. References to or inclusion of format
specifications in registration proposals is encouraged but not
required.
Format specifications are still required for registration in the
personal tree, but may be either published as RFCs or otherwise
deposited with IANA. The deposited specifications will meet the same
criteria as those required to register a well-known TCP port and, in
particular, need not be made public.
Some media types involve the use of patented technology. The
registration of media types involving patented technology is
specifically permitted. However, the restrictions set forth in RFC
1602 on the use of patented technology in standards-track protocols
must be respected when the specification of a media type is part of a
standards-track protocol.
2.2.5. Interchange Recommendations
Media types should, whenever possible, interoperate across as many
systems and applications as possible. However, some media types will
inevitably have problems interoperating across different platforms.
Problems with different versions, byte ordering, and specifics of
gateway handling can and will arise.
Universal interoperability of media types is not required, but known
interoperability issues should be identified whenever possible.
Publication of a media type does not require an exhaustive review of
interoperability, and the interoperability considerations section is
subject to continuing evaluation.
These recommendations apply regardless of the registration tree
involved.
2.2.6. Security Requirements
An analysis of security issues is required for for all types
registered in the IETF Tree. (This is in accordance with the basic
requirements for all IETF protocols.) A similar analysis for media
types registered in the vendor or personal trees is encouraged but
not required. However, regardless of what security analysis has or
has not been done, all descriptions of security issues must be as
accurate as possible regardless of registration tree. In particular,
a statement that there are "no security issues associated with this
Freed, et. al. Best Current Practice [Page 8]
RFC 2048 MIME Registration Procedures November 1996
type" must not be confused with "the security issues associates with
this type have not been assessed".
There is absolutely no requirement that media types registered in any
tree be secure or completely free from risks. Nevertheless, all
known security risks must be identified in the registration of a
media type, again regardless of registration tree.
The security considerations section of all registrations is subject
to continuing evaluation and modification, and in particular may be
extended by use of the "comments on media types" mechanism described
in subsequent sections.
Some of the issues that should be looked at in a security analysis of
a media type are:
(1) Complex media types may include provisions for
directives that institute actions on a recipient's
files or other resources. In many cases provision is
made for originators to specify arbitrary actions in an
unrestricted fashion which may then have devastating
effects. See the registration of the
application/postscript media type in RFC 2046 for
an example of such directives and how to handle them.
(2) Complex media types may include provisions for
directives that institute actions which, while not
directly harmful to the recipient, may result in
disclosure of information that either facilitates a
subsequent attack or else violates a recipient's
privacy in some way. Again, the registration of the
application/postscript media type illustrates how such
directives can be handled.
(3) A media type might be targeted for applications that
require some sort of security assurance but not provide
the necessary security mechanisms themselves. For
example, a media type could be defined for storage of
confidential medical information which in turn requires
an external confidentiality service.
2.2.7. Usage and Implementation Non-requirements
In the asynchronous mail environment, where information on the
capabilities of the remote mail agent is frequently not available to
the sender, maximum interoperability is attained by restricting the
number of media types used to those "common" formats expected to be
widely implemented. This was asserted in the past as a reason to
Freed, et. al. Best Current Practice [Page 9]
RFC 2048 MIME Registration Procedures November 1996
limit the number of possible media types and resulted in a
registration process with a significant hurdle and delay for those
registering media types.
However, the need for "common" media types does not require limiting
the registration of new media types. If a limited set of media types
is recommended for a particular application, that should be asserted
by a separate applicability statement specific for the application
and/or environment.
As such, universal support and implementation of a media type is NOT
a requirement for registration. If, however, a media type is
explicitly intended for limited use, this should be noted in its
registration.
2.2.8. Publication Requirements
Proposals for media types registered in the IETF tree must be
published as RFCs. RFC publication of vendor and personal media type
proposals is encouraged but not required. In all cases IANA will
retain copies of all media type proposals and "publish" them as part
of the media types registration tree itself.
Other than in the IETF tree, the registration of a data type does not
imply endorsement, approval, or recommendation by IANA or IETF or
even certification that the specification is adequate. To become
Internet Standards, protocol, data objects, or whatever must go
through the IETF standards process. This is too difficult and too
lengthy a process for the convenient registration of media types.
The IETF tree exists for media types that do require require a
substantive review and approval process with the vendor and personal
trees exist for those that do not. It is expected that applicability
statements for particular applications will be published from time to
time that recommend implementation of, and support for, media types
that have proven particularly useful in those contexts.
As discussed above, registration of a top-level type requires
standards-track processing and, hence, RFC publication.
2.2.9. Additional Information
Various sorts of optional information may be included in the
specification of a media type if it is available:
(1) Magic number(s) (length, octet values). Magic numbers
are byte sequences that are always present and thus can
be used to identify entities as being of a given media
Freed, et. al. Best Current Practice [Page 10]
RFC 2048 MIME Registration Procedures November 1996
type.
(2) File extension(s) commonly used on one or more
platforms to indicate that some file containing a given
type of media.
(3) Macintosh File Type code(s) (4 octets) used to label
files containing a given type of media.
Such information is often quite useful to implementors and if
available should be provided.
2.3. Registration Procedure
The following procedure has been implemented by the IANA for review
and approval of new media types. This is not a formal standards
process, but rather an administrative procedure intended to allow
community comment and sanity checking without excessive time delay.
For registration in the IETF tree, the normal IETF processes should
be followed, treating posting of an internet-draft and announcement
on the ietf-types list (as described in the next subsection) as a
first step. For registrations in the vendor or personal tree, the
initial review step described below may be omitted and the type
registered directly by submitting the template and an explanation
directly to IANA (at iana@iana.org). However, authors of vendor or
personal media type specifications are encouraged to seek community
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -