RFC 6648: 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.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community."""
"""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.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community."""