NETMOD Working Group L. Lhotka
Internet-Draft CZ.NIC
Intended status: Standards Track March 09, 2017
Expires: September 10, 2017
Using Markup in YANG Text Arguments
draft-lhotka-netmod-yang-markup-00
Abstract
This document defines a YANG extension that allows for specifying a
media type for text in the arguments of these YANG statements:
"contact", "description", "error-message", "organization" and
"reference."
Status of This Memo
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Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Declaring the Media Type of Text Arguments . . . . . . . . . 3
4. YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Descriptions play an important role in YANG data models. They may
specify normative semantic constraints that cannot be expressed
formally, instructions for implementors of the data model, and other
vital information. That is why descriptions often comprise several
paragraphs of text and sometimes also other structures such all
numbered or bulleted lists.
So far, YANG modules have mostly used only plain text in the argument
of the "description" statement, i.e., formatted text structures using
just whitespace. This is generally sufficient for human readers and
also for including YANG modules in RFC documents, but less so for
tools that are designed to process or use YANG modules in other ways,
for example:
o converting YANG compact syntax to other formats (YIN, HTML)
o including YANG modules in standards and other documents whose
source form in not plain text
o including description text in user interface elements.
The above considerations also apply, albeit to a lesser extent, to
other YANG statements with more structured arguments: "contact",
"error-message", "organization" and "reference".
In principle, it is possible to use any kind of markup such as
markdown [RFC7764] but doing so would not be not very effective and
tool-friendly unless the markup format is either standardized or
declared in the module source.
This document defines a YANG extension statement, "text-media-type",
that can be placed as a substatement of the "module" or "submodule"
statement to indicate the media type that is used throughout the
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(sub)module for markup in the arguments of the five YANG statements
mentioned above.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Declaring the Media Type of Text Arguments
Section 4 below contains the "ietf-yang-text-media-type" module that
defines a YANG language extension: "text-media-type". Its purpose is
to declare media type that is used for markup in the arguments of the
following YANG statements:
o contact
o description
o error-message
o organization
o reference
The common characteristic of these five statements is that their
argument is represented as the <text> element in YIN format
(Section 13 of [RFC7950]).
The "text-media-type" extension is intended to be used at the top
level of a YANG module or submodule, i.e., as a substatement of
either "module" or "submodule" statement. The declared media type
applies to arguments of the above YANG statements throughout the
module or submodule.
The "text-media-type" extension MAY be ignored, and a module in which
it appears MUST be valid YANG.
The argument of the "text-media-type" extension is a string
specifying the media type in the format defined in [RFC6838]. The
media type SHOULD be registered by IANA in the "text" registry
[IANA-MEDIA-TYPES]. Media type parameters MAY be used.
It is RECOMMENDED to use only media types representing "lightweight"
markup that is easy to read even in the unprocessed source form, such
as "text/markdown".
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YANG modules have to be use the UTF-8 character encoding, see
Section 6 of [RFC7950]. This implies the following rules:
o Whenever the "charset" parameter is present, its value MUST be
"UTF-8".
o If no default value is defined for the "charset" parameter of a
given media type, or if a default value is defined but is
different from "UTF-8", then the "charset" parameter MUST be
present with the value of "UTF-8".
Even if the "text-media-type" extension statement is present and
markup used in text arguments, all YANG and YIN syntax rules still
apply.
The "ietf-yang-text-media-type" module not only defines but also uses
the "text-media-type" extension statement, which illustrates its
typical use.
4. YANG Module
RFC Editor: In this section, replace all occurrences of 'XXXX' with
the actual RFC number and all occurrences of the revision date below
with the date of RFC publication (and remove this note).
<CODE BEGINS> file "ietf-yang-text-media-type@2017-03-09.yang"
module ietf-yang-text-media-type {
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-text-media-type";
prefix ymt;
ymt:text-media-type "text/markdown; charset=UTF-8";
organization
"IETF NETMOD (NETCONF Data Modeling Language) Working Group";
contact
"WG Web: <https://tools.ietf.org/wg/netmod/>
WG List: <mailto:netmod@ietf.org>
WG Chair: Lou Berger
<mailto:lberger@labn.net>
WG Chair: Kent Watsen
<mailto:kwatsen@juniper.net>
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Editor: Ladislav Lhotka
<mailto:lhotka@nic.cz>";
description
"This module defines the *text-media-type* extension that allows
for specifying media-type for markup that is used in arguments
of these YANG statements: contact, description, error-message,
organization, and reference.
Copyright (c) 2016 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject to
the license terms contained in, the Simplified BSD License set
forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and
'OPTIONAL' in the module text are to be interpreted as described
in RFC 2119 (https://tools.ietf.org/html/rfc2119).
This version of this YANG module is part of RFC XXXX
(https://tools.ietf.org/html/rfcXXXX); see the RFC itself for
full legal notices.";
revision 2017-03-09 {
description
"Initial revision.";
reference
"RFC XXXX: Using Markup in YANG Text Arguments";
}
extension text-media-type {
argument type;
description
"This extension allows for specifying a media type that is used
for markup in the arguments of the following YANG statements:
- contact
- description
- error-message
- organization
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- reference
The *text-media-type* extension statement MAY be used at the
top level of a module or submodule, i.e., as a substatement of
*module* or *submodule*, and no more than once. The declared
media type applies throughout the module or submodule.
The argument SHOULD be a media type registered by IANA in the
*text* registry. Media type parameters MAY be present.
This YANG extension is only indicative and optional to
implement. Tools MAY ignore it completely or support just a
subset of markup directives that are available for a given
media type.";
reference
"- IANA: Media Types, 2016-12-21. Available [online]
(http://www.iana.org/assignments/media-types/media-types.xhtml)
- [RFC 6838](https://tools.ietf.org/html/rfc6838): Media Type
Specifications and Registration Procedures";
}
}
<CODE ENDS>
5. IANA Considerations
RFC Editor: In this section, replace all occurrences of 'XXXX' with
the actual RFC number and all occurrences of the revision date below
with the date of RFC publication (and remove this note).
This document registers the following namespace URI in the "IETF XML
registry" [RFC3688]:
URI: urn:ietf:params:xml:ns:yang:ietf-yang-text-media-type
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace.
This document registers the following YANG module in the "YANG Module
Names" registry [RFC6020]:
Name: ietf-yang-text-media-type
Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-text-media-type
Prefix: ymt
Reference: RFC XXXX
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6. Security Considerations
The "text-media-type" extension defined in this document provides
information that is completely optional. YANG modules and submodules
in which it is present have to satisfy all rules of the YANG
language. The extension therefore doen't introduce any new threats.
7. References
7.1. Normative References
[IANA-MEDIA-TYPES]
Internet Assigned Numbers Authority, "Media Types", 12
2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<http://www.rfc-editor.org/info/rfc3688>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<http://www.rfc-editor.org/info/rfc6020>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<http://www.rfc-editor.org/info/rfc6838>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<http://www.rfc-editor.org/info/rfc7950>.
7.2. Informative References
[RFC7764] Leonard, S., "Guidance on Markdown: Design Philosophies,
Stability Strategies, and Select Registrations", RFC 7764,
DOI 10.17487/RFC7764, March 2016,
<http://www.rfc-editor.org/info/rfc7764>.
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Author's Address
Ladislav Lhotka
CZ.NIC
Email: lhotka@nic.cz
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