Merge branch 'master' into vpm-spec

Co-authored-by: Ram.Type-0 <39725073+RamType0@users.noreply.github.com>

docs/vpm-spec.md

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+# The VRChat Package Manager and vrc-get extensions.
+
+## Abstract
+
+The VRChat Package Manager (VPM) is a package manager architecture for UPM Packages
+developed by VRChat to distribute VRChat SDK based on Hypertext Transfer Protocol (HTTP).
+This document describes the overall architecture of VPM, 
+how the VPM Client should work, and how the package repository should provide packages 
+based on vrc-get developers' research.
+In addition, this document describes extensions of the VPM implemented by vrc-get.
+Please note that this document is not provided by VRChat, is provided by vrc-get developers, a third party VPM Client developers.
+
+## 1. Introduction
+### 1.1. Purpose
+The VRChat Package Manager is a package manager developed by VRChat and widely used by the VRChat community.
+However, the VRChat Creator Companion (VCC), the official VPM implementation, has several bugs that make it hard to know the VPM Client should work.
+Therefore, vrc-get developers assume the best VPM behavior based on the behavior of VCC, and [[VCC Docs]].
+This document describes the vrc-get developers' understanding of the VPM and vrc-get extensions
+for future VPM Client developers and VPM Repository developers.
+
+### 1.2. Core Concepts
+The VPM provides a simple way to distribute UPM packages.
+
+The VPM Repository provides a list of packages and their metadata, and the link to the package archive file, in JSON document hosted on the HTTP server.
+The VPM Repository can authorize VPM Clients by using Header-based authentication, including downloading the package archive file.
+
+The VPM Client is the software that manages the VPM Packages in the Unity project.
+The VPM Client fetches the package information from Package Repositories and collects packages to install based on requested packages, version constraints, and dependencies.
+The VPM Client then downloads the package archives from the URL provided by the Repository and extracts the package archive into `Packages` folder in the Unity project.
+The VPM Client also writes the managing package information to `Packages/vpm-manifest.json` to manage the installed packages.
+The VPM Client can re-install the package by using the information.
+This information is usually used to install packages after cloning the project with Version Control System.
+VPM Clients can share the user-wide installed repositories list and local package cache for better user experience.
+
+## 2. Conformance
+### 2.1. Syntax Notation
+This specification uses the Augmented Backus-Naur Form (ABNF) notation of [[RFC5234]].
+
+The following core rules are included by reference, as defined in Appendix B.1 of [[RFC5234]]: 
+ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls), DIGIT (decimal 0-9), DQUOTE (double quote), 
+HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed), OCTET (any 8-bit sequence of data), SP (space), 
+and VCHAR (any visible US-ASCII character).
+
+### 2.2. Requirements Notation
+The key words "**MUST**", "**MUST NOT**", "**REQUIRED**", "**SHALL**", "**SHALL NOT**", "**SHOULD**", 
+"**SHOULD NOT**", "**RECOMMENDED**", "**NOT RECOMMENDED**", "**MAY**", and "**OPTIONAL**" 
+in this document are to be interpreted as described in BCP 14 [[RFC2119]] [[RFC8174]] when, 
+and only when, they appear in all capitals, as shown here.
+
+## 3. Terminology and Core Semantics
+### 3.1. The UPM, UPM Package
+The UPM is the Unity Package Manager,
+which is the package manager developed by Unity Technologies and built into Unity Editor.
+The UPM provides the package management system for Unity Editor.
+
+The UPM Package is the package recognized by the UPM and Unity Editor.
+There are several ways to install UPM Packages to a Unity Project,
+but for VPM, the embedded UPM Package is the most important.
+The embedded UPM Package is the package that is placed in the `Packages` folder in the Unity project.
+
+All VPM Packages are recognized as embedded UPM Packages by Unity Editor.
+
+### 3.2. VPM, VPM Client, VPM Repository, VPM Profile Folder, and VPM Package
+The term "VPM" refers to the VRChat Package Manager, which is the package manager architecture.
+The VPM consists of the VPM Client and the VPM Repository.
+
+The VPM Client is the software that manages the VPM Packages in the Unity project.
+It fetches the package information from the VPM Repository and installs the package.
+
+The VPM Clients usually have feature to manage VPM Repository installed for the VPM Manifest folder.
+The VPM Client **MAY** have feature to add VPM Repository from Web Browsers by using the `vcc:` URL scheme.
+
+The VPM Repository is a [[JSON]] file on a HTTP(S) Server that provides package manifest and URL to the package archive.
+
+As described above, the VPM Client and VPM Repository communicate with each other via HTTP [[HTTP]].
+
+VPM Profile Folder is the folder that contains the configuration files and the cache files of the VPM Client.
+The configuration file for VPM Client should be shared among the VPM Clients because it contains the user-wide installed repositories list.
+However, the VPM Client **MAY** have different configuration files for some purposes, such as beta testing.
+Actually, the recent VCC Beta uses their own folder as the VPM Profile Folder.
+
+The VPM Package is the package distributed by the VPM.
+The VPM Package will be recognized as a UPM Package by Unity Editor.
+Therefore, the VPM Package is a special type of UPM Package.
+
+### 3.3. UPM Package Manifest, VPM Package Manifest, VPM Project Manifest
+The UPM Package Manifest is the JSON document that describes the package information.
+The UPM Package Manifest is located as `package.json` in the UPM Package and provides the package information,
+such as the package name, version, UPM dependencies.
+
+The VPM Package Manifest is a UPM Package Manifest that may have information for VPM.
+In addition to the UPM Package Manifest,
+the VPM Package Manifest provides the vpm dependencies and other data used by VPM.
+
+The VPM Project Manifest is the JSON document that describes the installed package information.
+The VPM Project Manifest is located as `Packages/vpm-manifest.json` in the Unity project and provides the installed package information,
+The VPM Project Manifest has two main sections, `dependencies` and `locked`.
+The `dependencies` section provides the requested package information.
+The `locked` section provides the all installed package information, including the dependencies of the requested packages.
+
+### 3.4. Requested Package, Dependency Package, Locked Package, and Unlocked Package
+Requested packages are VPM Packages that the user requested to install.
+The VPM client will tries to install those packages.
+
+Dependency packages are VPM packages that are required to install the requested packages.
+VPM Client automatically installs dependency packages when installing the requested package.
+
+Locked packages are embedded UPM packages that are controlled by the VPM Client.
+VPM Client manages locked packages based on the VPM Manifest.
+All requested packages and Dependency Packages are locked packages.
+
+Unlocked packages are the embedded UPM packages that are not controlled by the VPM Client.
+VPM Client does not modify unlocked packages.
+However, may read the package information from the UPM Package Manifest.
+
+## 4. VPM Package and Manifest
+This section describes the overall structure of VPM Package and the structure of the VPM Package Manifest.
+
+### 4.1. Overall Structure of VPM Package
+The VPM Package is a directory that contains the VPM Package Manifest file
+(named `package.json`) and the entries of the package.
+
+VPM Package **MUST** include file named `package.json` in the root directory of the package.
+VPM Package consists of files and directories,
+and they will be recognized as contents of the UPM Package by Unity Editor.
+
+VPM Package **SHOULD NOT** contain the file-system entries other than files and directories such as symbolic links and device files.
+
+All entries of the VPM Package **MUST** name with Unicode [[UNICODE]] characters
+and **MUST NOT** include any characters that are not allowed in the file system.
+All entries of the VPM Package **SHOULD NOT** use characters other than ASCII Alphabets, 
+Digits, Hyphen (`-`), Underscore (`_`), Space (` `), Dot (`.`), and Parentheses (`(`, `)`).
+Other characters can cause problems in some environments.
+
+> [!NOTE]
+> 
+> The rules about the file name are not provided in the [[VCC Docs]]
+>, and this is completely based on the vrc-get developers' research and opinion.
+> 
+> The official VCC uses .NET, so they cannot handle file names with non-UNICODE characters.
+> Therefore, we wrote the rule that entry name MUST name with Unicode characters.
+> 
+> For non-UTF-8 environments, Unity is unstable with non-ASCII characters.
+> Therefore, we wrote the rule that entry name SHOULD NOT use characters other than ASCII characters.
+> 
+> For some OSes like Windows, some characters are not allowed in the file name.
+> Therefore, we wrote the rule that entry name SHOULD NOT use characters other than specified characters.
+
+### 4.2. Structure of VPM Package Manifest
+VPM Package Manifest is a [[JSON]] document that describes the package information.
+The document **MUST** be named `package.json` and located in the root directory of the VPM Package.
+The document **MUST** be encoded in UTF-8 [[UNICODE]].
+VPM Package Manifest is a subset of the UPM Package Manifest.
+Some fields are required, and some fields are optional.
+Additional fields are allowed, so the VPM Client **SHOULD NOT** cause error with them.
+Some VPM Clients **MAY** use the additional fields for their purposes.
+
+#### 4.2.1. Basic Fields
+The VPM Package Manifest **MUST** include the following two fields.
+
+##### 4.2.1.1. `name` (string)
+The `name` field shows the globally unique ID of the package.
+The type of this field **MUST** be a string.
+
+The package ID is used to identify single package, so this **MUST** be unique among all packages in the VPM Repository
+and **SHOULD** be unique among all packages in the VPM ecosystem.
+VPM client will treat packages with same ID as same package.
+
+The Package ID **SHOULD** be prefixed with reverse domain name of the package author to be unique.
+
+The package ID **SHOULD** be in lowercase and **MUST NOT** contain any characters other than ASCII Alphabets, Digits, Hyphen (`-`), and Dot (`.`).
+The VPM Client **MAY** allow the package name that does not follow the rule.
+
+##### 4.2.2.2. `version` (string)
+The `version` field shows the version of the package.
+The type of this field **MUST** be a string.
+The value of this field **MUST** follow the Semantic Versioning 2.0.0 [[SEMVER]].
+Because the UPM doesn't support that, the `version` **MUST NOT** include the build metadata.
+The VPM Client **MAY** support a loose version like `"1.0"`, `"  v1.0.0 "` or `"v1.0.0"`,
+however, some VPM Clients **MAY** ignore the packages with a loose version.
+
+> [!NOTE]
+> 
+> The VCC currently does support the loose versions.
+> This came from the underlying library of the VCC, `semver.net` by Adam Reeve (https://github.com/adamreeve/semver.net)
+> In the future version of `semver.net`, accepting a loose version is going to be removed 
+> so that the VCC may remove support the loose versions in the future.
+>
+> On the other hand, the vrc-get does not support the loose versions.
+> This is originally came from the `semver` crate by David Tolnay.
+
+#### 4.2.3. Package Resolution Fields
+The VPM Package Manifest **MAY** include the following fields.
+Those fields are used to determine the package is compatible with the Project and find dependency packages.
+
+##### 4.2.3.1. `vpmDependencies` (object)
+The `vpmDependencies` field shows the dependencies of the package.
+The type of this field **MUST** be an object. 
+
+The key of this field **MUST** be the package name,
+and the value **MUST** be a string that describes the version constraint.
+The format of the version constraint will be described in [!TODO:Section Version Constraint in Package Resolving].
+
+The VPM Client will resolve the dependencies of the package based on this field.
+More about the resolving process will be described in [!TODO:Section Package Resolving].
+
+##### 4.2.3.2. `unity` (string)
+The `unity` field shows the minimum Unity version that the package is compatible with.
+The type of the this field **MUST** be a string.
+The value of this field **MUST** follow the Unity Version number described in [!TODO:Section Unity Version in Package Resolving].
+
+The VPM Client will check the compatibility of the package with the Unity Project based on the `unity` field.
+If the package is not compatible with the Unity Project,
+the VPM Client **MUST** reject the installation of the package or show a warning to the user. 
+
+##### 4.2.3.3. `legacyPackages` (array)
+The `legacyPackages` field shows the list of legacy packages that the package name is replacing.
+The type of this field **MUST** be an array of strings.
+
+The UdonSharp and ClientShim was provided as a separate package in the past
+and since VRCSDK 3.4.0, they are provided as a part of the VRCSDK.
+However, at that time, many packages are depending on the UdonSharp and ClientShim.
+Therefore, VRChat introduced the `legacyPackages` field to provide the compatibility with the old packages.
+
+The VPM Client **MUST** guarantee
+that packages specified in the `legacyPackages` field are not installed when the package is installed.
+
+#### 4.2.4. Installation Data Fields
+The VPM Package Manifest **MAY** include the following fields that are used to install the package.
+
+##### 4.2.4.1. `url` (string)
+The `url` field shows the URL of the package archive file.
+The type of this field **MUST** be a string.
+The value of this field **MUST** be a valid URL that points to the package archive file.
+The VPM Package Manifest in the Remote Package Repository **MUST** include the `url` field with the valid URL.
+
+The VPM Client will download the package archive file from the URL specified with this field.
+If the `url` field is not included in the VPM Package Manifest,
+the VPM Client **MUST** reject the installation of the package.
+
+The VPM Repository **MUST NOT** change the contents of the URL this field points to. this is compared bitwisely.
+
+> [!NOTE]
+> 
+> Unfortunately, some known popular repository did change the contents of repository so it might be better to assume packages might change.
+
+##### 4.2.4.2. `zipSHA256` (string)
+The `zipSHA256` field shows the SHA-256 hash of the package archive file.
+The type of the `zipSHA256` field **MUST** be a string.
+The `zipSHA256` field **MUST** be a valid HEXDIG encoded SHA-256 hash of the package archive file.
+Typically the output of sha256sum.
+
+The VPM Client **MUST** use this hash to verify the integrity of the cached package archive file.
+and **MAY** use this hash to verify the integrity of the downloaded package archive file.
+
+The VPM Client **MAY** reject the installation of the package
+if the downloaded package does not match the SHA-256 hash specified in the `zipSHA256` field.
+
+##### 4.2.4.3. `headers` (object)
+The `headers` field shows the additional HTTP headers that is for fetching the package archive file.
+The type of the `headers` field **MUST** be an object, and the keys and values **MUST** be strings.
+
+The VPM Client **MUST** add the headers specified in the `headers` field to fetch the package archive file.
+
+#### 4.2.5. Human-readable Fields
+The VPM Package Manifest **MAY** include the following fields that are used to provide Human-readable information of the package.
+Those fields **MUST NOT** affect the behavior of the VPM Client except for errors on type mismatch.
+
+##### 4.2.5.1. `displayName` (string)
+The `displayName` field shows the human-readable name of the package.
+The type of the `displayName` field **MUST** be a string.
+The `displayName` field should show the human-readable name of the package.
+The name is usually in English but may be in other languages.
+
+##### 4.2.5.2. `description` (string)
+The `description` field shows the human-readable description of the package.
+The type of the `description` field **MUST** be a string.
+The `description` field should show the human-readable description of the package.
+The name is usually in English but may be in other languages.
+
+##### 4.2.5.3. `changelogUrl` (string)
+The `changelogUrl` field shows the URL of the changelog of the package.
+The type of the `changelogUrl` field **MUST** be a string.
+The `changelogUrl` field **SHOULD** be a valid URL that points to the changelog of the package.
+The VPM Client **MAY** suggest users to open the URL with the Web Browser when the package is updated.
+
+#### 4.2.A. `vrc-get` extension (object)
+The VPM Package Manifest **MAY** include the `vrc-get` object that is used to provide the additional information for the vrc-get.
+The `vrc-get` object **MUST** be an object.
+The VPM Client **MAY** ignore the `vrc-get` object.
+The `vrc-get` object **MAY** include the following fields.
+
+##### 4.2.A.1. `vrc-get.yanked` (string or boolean)
+The `yanked` field shows the yanked status of the package.
+The type of the this field **MUST** be a non-empty string or boolean.
+If this field is a string, the package is yanked and the string **MUST** be the reason of the yanked.
+If this field is a boolean, the package is yanked if the value is `true` and not yanked if the value is `false`.
+
+The VPM Clients that recognizes this field **SHOULD** show the warning
+if the package is yanked and the package is already installed
+and **MUST** deny installing yanked packages except for resolving the packages.
+
+##### 4.2.A.2. `vrc-get.aliases` (array)
+The `vrc-get.aliases` field shows the list of the alternative package display names.
+The type of this field **MUST** be an array of strings.
+The VPM Client **MAY** use this field to better package search
+but this field **MUST NOT** affect the behavior of the VPM Client.
+
+## 5. VPM Repository
+The VPM Repository is a JSON file on a HTTP server that provides package manifest and the URL to the VPM Package Archive.
+The user provides the URL and Headers information to the VPM Client to access the VPM Repository.
+
+This section describes not only about contents of VPM Repository JSON file, but also about archive file VPM Repository points to.
+
+### 5.1.  VPM Repository JSON
+VPM Repository **MUST** be a JSON file encoded in UTF-8 [[UNICODE]] and **MUST** be an object that contains the following fields.
+
+#### 5.1.1. `packages` (object)
+The `packages` field shows the list of packages in the VPM Repository.
+The type of this field **MUST** be an object.
+The key of the value of this field **MUST** be the package ID
+and the value **MUST** be an object that contains the following fields.
+
+##### 5.1.1.1. `packages.<id>.versions` (object)
+The `packages.<id>.versions` field shows the list of versions of the package.
+The type of this field **MUST** be an object.
+The key of the value of this field **MUST** be the version of the package,
+which is a valid version name described in Semantic Versioning 2.0.0 [[SEMVER]].
+
+The value **MUST** be an object that contains the VPM Package Manifest,
+which is described in [Section 4.2](#42-structure-of-vpm-package-manifest).
+
+The VPM Package Manifest **MUST** have same package ID as the key of `packages` object,
+and same version as the key of `packages.<id>.versions` object.
+The VPM Package Manifest **MUST** have the `url` field that points to the package archive file.
+
+#### 5.1.2. `url` (string)
+The `url` field shows the URL of the VPM Repository JSON.
+The type of this field **MUST** be a string.
+The value of this field **MUST** be a valid URL that points to the VPM Repository JSON.
+
+According to The [[VCC Docs]], It should point to the VPM Repository JSON.
+However, for Some existing VPM Repositories,
+the `url` field is used to point some related pages like booth page or the Author's Website.
+Therefore, VPM Client **SHOULD NOT** use the `url` field to fetch the VPM Repository JSON.
+
+#### 5.1.3. `id` (string)
+The `id` field shows the unique identifier of the VPM Repository.
+The type of this field **MUST** be a string.
+VPM Repository **SHOULD** provide the `id` field to identify the VPM Repository.
+If the `id` field is not provided, the VPM Client use the URL of the VPM Repository as the `id` field.
+
+The `id` field **MUST** be unique among all VPM Repositories.
+To the `id` field be unique among all repositories in the VPM ecosystem, 
+the `id` **SHOULD** be prefixed with reverse domain name of the VPM Repository author.
+
+#### 5.1.4. `name` (string)
+The `name` field shows the human-readable name of the VPM Repository.
+The type of the `name` field **MUST** be a string.
+The `name` field should show the human-readable name of the VPM Repository.
+
+#### 5.1.5. `author` (string)
+The `author` field shows the human-readable author of the VPM Repository.
+The type of the `author` field **MUST** be a string.
+The `author` field should show the human-readable author of the VPM Repository.
+
+> [!NOTE]
+> 
+> In the VRChat Official Repository at <https://packages.vrchat.com/official?download> and other popular repositories 
+> the `author` field shows the name of the organization or the group that manages the repository.
+> 
+> On the other hand, in the Example Repository in the [[VCC Docs]],
+> the `author` field shows the email address of the author.
+>
+> We don't know the reason for this difference, but We think the `author` field should show the human-readable name of the author.
+> It's more user-friendly and easier to understand.
+
+### 5.2. Package Archive File
+The Package Archive File is a Zip archive file that contains the package contents.
+The Package Manifest inside the Package Repository JSON **MUST** have the `url` field
+that points to the Package Archive File.
+
+The paths in the Package Archive File **MUST** be encoded in UTF-8 [[UNICODE]]. It's not necessary to set Language Encoding flag in zip.
+
+The root directory of the Package Archive File is the root directory of the VPM Package.
+In other words, `package.json` of the VPM Package will be located as `package.json` in the Package Archive File,
+not as `package/package.json` or `root/package.json`.
+
+The VPM Package **MUST** use `/` as path separator, **MUST NOT** include paths starting with `/` (absolute path) or `../` (path traversal), or contains `\\` (Windows path separator), `/../` (path traversal), `/./` (path identity in archive), or `:` (Windows drive letter which can cause absolute path).
+
+The VPM Client **MUST** support compression method 0 (stored) and 8 (deflate). Package Archive Files **SHOULD NOT** use compression Methods other than 0 or 8.
+
+> [!NOTE]
+> 
+> Notes for the VPM Package Developers
+> 
+> In the recent OSes, when we compress a directory, they create root directory that contains the directory.
+> Therefore, please be careful when you compress your VPM Package.
+>
+> In addition, you should not use Windows Explorer to create zip files since it may use deflate64, which will cause compatibility problems.
+
+> [!NOTE]
+> Notes About Deflate64 Compression Method
+> 
+> For better compatibility, the VPM Archive File should not use the compression method other than Deflate.
+> 
+> Most implementation of Zip file only supports the Deflate compression method or store uncompressed bytes.
+> For example, the standard library of go, python,
+> and java only supports the Deflate compression method and uncompressed bytes.
+> 
+> However, the Microsoft Windows built-in Zip file compressor may use the Deflate64 compression method.
+> The Deflate64 compression method is not supported by most of the Zip file implementations.
+> As a result, some existing VPM Packages may use the Deflate64 compression method in their Package Archive File.
+> Therefore, it might be better for VPM Clients to support the Deflate64 compression method.
+> 
+> Side Note: the Deflate64 compression method is not publicly documented.
+> In the APPNOTE.TXT by pkware, deflate64 is described as "Deflate64(tm) is supported by the Deflate extractor.",
+> but it requires larger window size and no literal to code mapping on document, so it's impossible to decompress with existing Deflate implementation.
+> In addition, the Deflate64 is not documented in any public documents,
+> so there are very limited deflate 64 implementations.
+> Here's an incomplete list of known open-source implementations:
+> - [.NET System.IO.Compression](https://github.com/dotnet/runtime/blob/2f08fcbfece0c09319f237a6aee6f74c4a9e14e8/src/libraries/System.IO.Compression/src/System/IO/Compression/DeflateManaged/) by Microsoft, inc. under the MIT License
+> - [7zip](https://sourceforge.net/projects/sevenzip/files/7-Zip/) by Igor Pavlov under the GNU LGPL 2.1
+> - [deflate64-rs](https://github.com/anatawa12/deflate64-rs) by anatawa12 based which is reimplementation of the .NET System.IO.Compression under the MIT License
+> - [Info Zip](https://sourceforge.net/projects/infozip/) by Info-ZIP under the Info-ZIP License
+> - [Apache Commons Compress](https://commons.apache.org/proper/commons-compress/) by Apache Software Foundation under the Apache License 2.0
+
+## References
+### \[VCC Docs]
+VRChat provides documentation for VCC at https://vcc.docs.vrchat.com/.
+The document is also published on GitHub at https://github.com/vrchat-community/creator-companion.
+This spec is based on commit [2f09cfe](https://github.com/vrchat-community/creator-companion/tree/2f09cfef3734b34e6e2cf4d8107c955c4f123322).
+
+### \[HTTP]
+Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, June 2022, <<https://www.rfc-editor.org/info/rfc9110>>.
+
+### \[JSON]
+Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, December 2017, <<https://www.rfc-editor.org/info/rfc8259>>.
+
+### \[UNICODE]
+Unicode Consortium, "The Unicode Standard", <<https://www.unicode.org/versions/latest/>>.
+
+### \[SEMVER]
+Preston-Werner, T., "Semantic Versioning 2.0.0", <<https://semver.org/spec/v2.0.0.html>>.
+
+### \[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>>.
+
+### \[RFC5234]
+Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008, <<https://www.rfc-editor.org/info/rfc5234>>.
+
+### \[RFC8174]
+Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <<https://www.rfc-editor.org/info/rfc8174>>.
+
+[VCC Docs]: #vcc-docs
+[HTTP]: #http
+[JSON]: #json
+[SEMVER]: #semver
+[UNICODE]: #unicode
+[RFC5234]: #rfc5234
+[RFC2119]: #rfc2119
+[RFC8174]: #rfc8174