HTTP Accept header中的“+”是什么意思？
What does "+" means in HTTP Accept header?
我怎么理解这条记录：
Accept: application/vnd.my.api+json
我的意思是，这个“+”符号是标准化的（无论如何，我没有在规范中找到它），还是只是一种约定？
谢谢。
Accept header 指定可接受媒体类型的列表。
媒体类型的“+xxx”部分称为后缀。它是对媒体类型定义的扩充，有助于指定该媒体类型的底层结构。
RFC 6838，《4.2.8.结构化语法名称后缀》定义：
XML in MIME [RFC3023] defined the first such augmentation to the
media type definition to additionally specify the underlying
structure of that media type. To quote:
This document also standardizes a convention (using the suffix
'+xml') for naming media types ... when those media types
represent XML MIME (Multipurpose Internet Mail Extensions)
entities.
That is, it specified a suffix (in that case, "+xml") to be
appended to the base subtype name.
Since this was published, the de facto practice has arisen for
using this suffix convention for other well-known structuring
syntaxes. In particular, media types have been registered with
suffixes such as "+der", "+fastinfoset", and "+json". This
specification formalizes this practice and sets up a registry for
structured type name suffixes.
The primary guideline for whether a structured type name suffix is
registrable is that it be described by a readily available
description, preferably within a document published by an established
standards-related organization, and for which there's a reference
that can be used in a Normative References section of an RFC.
Media types that make use of a named structured syntax SHOULD use
the appropriate registered "+suffix" for that structured syntax
when they are registered. By the same token, media types MUST NOT
be given names incorporating suffixes for structured syntaxes they
do not actually employ. "+suffix" constructs for as-yet
unregistered structured syntaxes SHOULD NOT be used, given the
possibility of conflicts with future suffix definitions.
我怎么理解这条记录：
Accept: application/vnd.my.api+json
我的意思是，这个“+”符号是标准化的（无论如何，我没有在规范中找到它），还是只是一种约定？
谢谢。
Accept header 指定可接受媒体类型的列表。 媒体类型的“+xxx”部分称为后缀。它是对媒体类型定义的扩充，有助于指定该媒体类型的底层结构。
RFC 6838，《4.2.8.结构化语法名称后缀》定义：
XML in MIME [RFC3023] defined the first such augmentation to the
media type definition to additionally specify the underlying
structure of that media type. To quote:This document also standardizes a convention (using the suffix '+xml') for naming media types ... when those media types represent XML MIME (Multipurpose Internet Mail Extensions) entities.That is, it specified a suffix (in that case, "+xml") to be appended to the base subtype name.
Since this was published, the de facto practice has arisen for using this suffix convention for other well-known structuring syntaxes. In particular, media types have been registered with suffixes such as "+der", "+fastinfoset", and "+json". This specification formalizes this practice and sets up a registry for structured type name suffixes.
The primary guideline for whether a structured type name suffix is registrable is that it be described by a readily available
description, preferably within a document published by an established standards-related organization, and for which there's a reference
that can be used in a Normative References section of an RFC.Media types that make use of a named structured syntax SHOULD use the appropriate registered "+suffix" for that structured syntax when they are registered. By the same token, media types MUST NOT be given names incorporating suffixes for structured syntaxes they do not actually employ. "+suffix" constructs for as-yet unregistered structured syntaxes SHOULD NOT be used, given the possibility of conflicts with future suffix definitions.