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Deprecating the "X-" Prefix and Similar Constructs in Application Protocols (RFC6648) Disclosure Number: IPCOM000219209D
Original Publication Date: 2012-Jun-01
Included in the Prior Art Database: 2012-Jun-26
Document File: 26 page(s) / 28K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

P. Saint-Andre: AUTHOR [+2]


Many application protocols use parameters with textual (as opposed to numerical) names to identify data (media types, header fields in Internet mail messages and HTTP requests, vCard parameters and properties, etc.). Historically, designers and implementers of application protocols have often distinguished between standardized and unstandardized parameters by prefixing the names of unstandardized parameters with the string "X-" or similar constructs (e.g., "x."), where the "X" is commonly understood to stand for "eXperimental" or "eXtension".

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Internet Engineering Task Force (IETF)                    P. Saint-Andre Request for Comments: 6648                           Cisco Systems, Inc. BCP: 178                                                      D. Crocker Category: Best Current Practice              Brandenburg InternetWorking ISSN: 2070-1721                                            M. Nottingham                                                                Rackspace                                                                June 2012

            Deprecating the "X-" Prefix and Similar Constructs                         in Application Protocols


   Historically, designers and implementers of application protocols    have often distinguished between standardized and unstandardized    parameters by prefixing the names of unstandardized parameters with    the string "X-" or similar constructs.  In practice, that convention    causes more problems than it solves.  Therefore, this document    deprecates the convention for newly defined parameters with textual    (as opposed to numerical) names in application protocols.

Status of This Memo

   This memo documents an Internet Best Current Practice.

   This document is a product of the Internet Engineering Task Force    (IETF).  It represents the consensus of the IETF community.  It has    received public review and has been approved for publication by the    Internet Engineering Steering Group (IESG).  Further information on    BCPs is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,    and how to provide feedback on it may be obtained at

 Saint-Andre, et al.       Best Current Practice                 [Page 1]
 RFC 6648                    Deprecating "X-"                   June 2012

 Copyright Notice

   Copyright (c) 2012 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    ( 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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