// Copyright 2014-2021 The Khronos Group Inc.
//
// SPDX-License-Identifier: CC-BY-4.0

= Vulkan^®^ Documentation and Extensions: Procedures and Conventions
Jon Leech, Tobias Hector
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[[introduction]]
= Introduction

This document contains required procedures and conventions when writing
specifications for new Vulkan APIs, extensions and layers, or related
Khronos^{reg}^ documentation such as white papers and tutorials; or
contributing to existing Vulkan specifications.
These are collectively referred to as _Vulkan Documentation_ or just
_documentation_ below.
The primary focus is the API Specification and API extensions, although all
of the markup and most of the writing style is equally applicable to other
documentation.

The primary purpose is to achieve consistency across the API, as well as
across all of our source and output documents.
Consistency makes it easier for developers, editors, reviewers, and users of
our documentation to understand and modify it.

This document is now formally voted on and approved by the Vulkan Working
Group.
This means that unless explicitly stated otherwise, the procedures and
conventions must be followed.
If you have a strong desire to modify the procedures and conventions, such
changes must be made through the normal Vulkan Working Group processes.


[[introduction-terminology]]
== Terminology

The key words *must*, *required*, *should*, *recommend*, *may*, and
*optional* in this document are to be interpreted as described in RFC 2119
and by the Vulkan Specification in the "`Terminology`" section.


[[introduction-structure]]
== Document Structure

The style guide is broken into four sections:

  * <<naming,API Naming Conventions>> - the required rules for choosing
    names of Vulkan identifiers of all types.
  * <<extensions,Extensions and Layers>> - the required procedures for
    creating formal Vulkan extensions and layers.
  * <<markup,Markup Style>> - the required and recommended markup style for
    writing asciidoctor and XML source that follows consistent formatting
    and layout guidelines, tags special terms and phrases for proper
    processing by the spec generation tools, etc.
  * <<writing,Writing Style>> - the required and recommended writing style
    for overall and fine-grained structure and conventions, normative
    language use, API naming conventions, common words and phrases to use
    and to avoid, linking and cross-referencing, etc.


[[introduction-asciidoc]]
== Asciidoctor Markup

Vulkan Documentation is primarily written in Asciidoctor, a text markup
language.
We use the command-line asciidoctor client that is actively maintained by
asciidoctor, which is documented on its website at https://asciidoctor.org.

References to the Asciidoctor User Manual are to sections in the document at
https://asciidoctor.org/docs/user-manual/.

Asciidoctor is implemented in Ruby (https://www.ruby-lang.org/), which is
available for Linux, MacOS, and Microsoft Windows.

[NOTE]
.Note
====
There are other implementations of asciidoctor, such as AsciidoctorJ
(https://github.com/asciidoctor/asciidoctorj) and asciidoctor.js
(https://github.com/asciidoctor/asciidoctor.js).
In particular, GitHub and GitLab both have preview renderers for .adoc or
.asciidoc files in repositories, and live preview extensions exist for
Chrome and Firefox.

However, because of the use of custom Ruby macros in the Vulkan
Specification toolchain, and the high complexity of the documents and
toolchain used to generate it, these web tools cannot currently render the
Specification from source.
Instead, we generate HTML and PDF versions of the Specification and publish
them on the Khronos website.

The Asciidoctor toolchain and build process are not addressed by this
document, which concentrates solely on source documents.
====


[[introduction-normative]]
== Normative References

Normative references are references to external documents or resources to
which documentation authors must comply.

[[acm-references]]
Association for Computing Machinery.
_Citation Style and Reference Formats_.
Retrieved July 27, 2019.
https://www.acm.org/publications/authors/reference-formatting .

[[iso-8601]]
International Organization for Standardization.
_Data elements and interchange formats -- Information interchange --
Representation of dates and times_ (2004-12-01).
https://www.iso.org/standard/40874.html .
Also see https://www.w3.org/QA/Tips/iso-date for colloquial examples.

[[vulkan-docs]]
Khronos Vulkan Working Group.
`KhronosGroup/Vulkan-Docs` project on GitHub (July 5, 2016).
https://github.com/KhronosGroup/Vulkan-Docs .

[[vulkan-spec]]
Khronos Vulkan Working Group.
_Vulkan 1.1.116 - A Specification_ (July 20, 2019).
https://www.khronos.org/registry/vulkan/ .

Version 1.1.116 is the latest patch release of the Vulkan API Specification
as of the time this reference was created, but that Specification is
frequently updated with minor bugfixes and clarifications.
When a more recent patch release is made, it becomes the normative reference
for the API.


// Chapters of the text are included below

include::style/naming.txt[]

include::style/extensions.txt[]

include::style/markup.txt[]

include::style/writing.txt[]

include::style/misc.txt[]

// Appendices are included below
include::style/vuid.txt[]


= Revision History

* 2021-07-20 - Add additional contraction examples to the table in the
  <<markup-avoid-contractions, Avoid Abbreviations and Contractions>>
  section.
* 2021-05-31 - Add "`implementation-dependent`" as an exception in the
  <<writing-compound-words, Compound Words and Preferred Orthography>>
  section (internal merge request 4611).
* 2021-05-24 - Add escapes to prevent expansion of attribute names in a few
  places where markup examples are given.
* 2021-05-22 - Expand the <<markup-avoid-contractions, markup rules>> to
  include avoiding abbreviations, as well as contractions.
* 2021-05-07 - Add <<markup-word-choices, preferred way to write
  "`drawing/dispatching command">>.
* 2021-04-28 - Add <<markup-word-choices, disambiguations for
  "`executable`">>.
* 2021-04-28 - Add <<writing-pointers-instances, usage for pointers and
  handles>> which may be `NULL` or dname:VK_NULL_HANDLE, respectively
  (internal issue 2662).
* 2021-04-14 - Add "`side effect`" and "`reuse`" as
  <<writing-compound-words, preferred orthography>> (public issue 1484).
* 2021-03-31 - Update description of the code{cl} macro in the
  <<markup-macros-api, API Markup Macros>> section to match current
  behavior.
* 2021-03-21 - Note that the <<extensions-reserving-bitmask-values same bit
  should be reserved>> for the same purpose in comparable 32- and 64-bit
  bitmask types (internal issue 2565).
* 2020-09-14 - Change <<markup-informative-notes, Informative Sections and
  Notes>> section to track actual usage and update the description of the
  undefined{cl} macro to further clarify its purpose and uses (internal
  issue 2195).
* 2020-08-16 - Add "`reference monitor`" to the preferred
  <<markup-word-choices, Word Choices>> (internal issue 2291).
* 2020-08-10 - Add a <<writing-describing-errors, Commands which Return
  Error Codes>> section to guide authors of new commands (internal issue
  2290).
* 2020-07-28 - Add a <<markup-copyrights, Copyrights and Licenses>> section
  describing how to properly attribute this information.
* 2020-06-23 - Update the <<extensions-documenting-extensions, Changes for
  New Extensions>> section to recommend placing most extension language
  inline in existing specification source files, rather than in separate
  files, and to base extension revision numbers at `1` starting with initial
  public release (public issue 1263).
* 2020-04-29 - Expand use of `basetype` macros to include external API
  types.
* 2020-03-16 - Add documentation of writing links to extension appendices in
  the <<extensions-documenting-extensions, Changes for New Extensions>>
  section and document the apiext{cl} and reflink{cl} macros in the
  <<markup-macros-api, API Markup Macros>> section.
  Improve documentation of writing <<writing-refpages, Markup For Automatic
  Reference Page Extraction>> including how to mark up content in the
  Specification source so it only appears in generated reference pages;
  however, this section is still out of date (internal issue 1999).
* 2020-03-11 - Specify in the <<sample-command, Sample Command Description>>
  section that a valid usage statement must be defined at the place (command
  or structure specification) that all information need to evaluate the
  statement is known.
  Update the description of <<appendix-vuid-creating, Creating VUID tags>>
  to match the current scripts.
  Use the term "`asciidoctor`" instead of "`asciidoc`" everywhere.
  Note in the <<introduction-asciidoc, Asciidoctor Markup>> section that the
  Specification can only be built using the command-line asciidoctor client,
  not by asciidoctor web clients.
* 2020-02-22 - Document that it is no longer needed to escape C arrows in
  macros.
* 2019-12-15 - Add a markup section on <<markup-macros-prime-symbols, Prime
  Symbols>> (internal issue 1110).
* 2019-11-27 - Expand the <<writing-pNext-chain, Describing Extension
  Structure Chains>> section and make all spec language consistent with it
  (internal issue 1814).
* 2019-09-09 - Define markup for nested structure members in the
  <<markup-macros-api, API Markup Macros>> section (internal issue 1765).
* 2019-09-08 - Add language to the end of the
  <<extensions-documenting-extensions, Changes for New Extensions>> section
  describing how to mark up asciidoctor conditionals (internal issue 1808).
* 2019-08-25 - Add the <<markup-indentation-equations, Indentation of
  Equations>> section (internal issue 1793).
* 2019-08-25 - Add the <<writing-describing-layers, Extensions and Grouping
  Related Language>> section (internal issue 979) and the
  <<markup-minimize-indentation, Minimize Indentation>> section (internal
  issue 747).
  Disallow use of standalone `+` except in latexmath and source blocks, in
  the <<markup-layout, Asciidoc Markup And Text Layout>> section (internal
  issue 736).
* 2019-08-19 - Add the <<writing-pointers-instances, Describing Pointers and
  Instances>> section (internal issue 1553).
* 2019-08-13 - Add a NOTE to the <<appendix-vuid-format, Format of VUID
  Tags>> appendix specifying allowed characters in VUID tags (based on
  discussion for internal merge request 3239).
* 2019-07-27 - Add the <<writing-references, References>> section and
  rewrite external references accordingly.
* 2019-05-09 - Specify rules for defining <<extensions-new-flags-types, new
  flags and bitmask types>> (internal issue 1649).
* 2019-01-06 - Add details on <<extensions-reserving-bitmask-values,
  Reserving Bitmask Values>> (internal issue 1411).
* 2018-11-19 - Add details to the <<extensions-documenting-extensions,
  Changes for New Extensions>> section including the new "`Description`"
  section, and other standard parts of extension appendices.
* 2018-08-13 - Add %inline directive to the <<markup-sample-section-images,
  Figures>> section (public pull request 734).
* 2018-07-30 - Added a section on <<writing-undefined, Describing Undefined
  Behavior>> (as part of the fixes for public issue 379), and describing why
  the undefined{cl} macro should always be used.
* 2018-07-08 - Remove requirement to explicitly include extension appendices
  in the <<extensions-documenting-extensions, Changes for New Extensions>>
  section.
* 2018-06-25 - Modify the process for <<extensions-vendor-id, Registering a
  Vendor ID with Khronos>> to define vendor ID values as part of an
  enumerated type.
* 2018-03-07 - Updated for Vulkan 1.1 release.
* 2018-01-10 - Move details of mandated extension compatibility from the
  <<extensions-rules, General Rules/Guidelines>> section into the
  Fundamentals section of the API Specification, where they are changed
  slightly to allow explicit incompatibilies (public issue 638).
* 2017-10-27 - Add language about proper use of "`valid pointer`" and
  "`pointer to valid object`" for valid usage statements, in the
  <<sample-command, Sample Command Description>> section (related to public
  pull request 547).
* 2017-10-15 - Describe how to write <<writing-latexmath-in-table-cells,
  LaTeX Math in Table Cells>> (internal issue 908).
* 2017-10-15 - Add more details of <<extensions-naming-author-IDs, `KHX`
  extensions>> (public issues 536, 580).
* 2017-09-10 - Add descriptions of <<writing-arrays, how to use `each` and
  `any`>> to refer to properties of elments of arrays (internal issue 884).
* 2017-09-10 - Add <<extensions-interactions-parent, Valid Usage and
  Extension pname:pNext Chains>> language specifying where to describe
  interactions of structures in a pname:pNext chain (internal issue 715).
* 2017-09-10 - Add example of marking up an enumerated type all of whose
  values are defined by extensions (internal issue 864).
* 2017-08-25 - Add language to the <<extensions,API Versions, Extensions,
  and Layers>> chapter describing how to write new API versions (internal
  issue 892).
* 2017-06-12 - Add sections describing when to use the
  <<markup-macros-api-name, *name{cl}>> and <<markup-macros-api-text,
  *text{cl}>> markup macros instead of the *link{cl} macros, and clarify
  that slink{cl} should be used for handle as well as structure names
  (internal issue 886).
* 2017-05-08 - Add appendix describing <<appendix-vuid, Valid Usage ID
  Tags>> and how they're generated.
* 2017-03-19 - Add naming rule for <<naming-extension-structures, Extension
  Structure Names>>.
* 2017-02-11 - Finish transitioning to asciidoctor markup.
* 2016-09-28 - Add asciidoc math markup guidelines.
* 2016-09-16 - Make style guide markup more consistent with its own
  recommendations.
  Simplify some tables of preferred terms.
  Add sections on block and table markup.
* 2016-09-12 - Describe writing and markup style for labelled lists.
  Require use of the ISO 8601 date format except in rare legacy cases.
  Expand the description of <<markup-layout,Line Lengths>> and add a
  description of markup for <<markup-footnotes,Footnotes>>.
* 2016-09-08 - Add a writing section about proper use of
  <<writing-misc-a-an,"`a`" and "`an`">> (internal issue 432).
* 2016-08-30 - Remove mustnot{cl} and shouldnot{cl} macro definitions, which
  are no longer used in the Specification (internal issue 407).
* 2016-08-29 - Add spelling and compound word rules (public issue 352).
* 2016-08-23 - Modify description of specifying extensions in the
  <<extensions,Layers and Extensions>> chapter to refer to the new
  single-branch model for extensions (internal issue 397).
* 2016-07-26 - Add section describing <<writing-refpages,markup for
  automatic reference page extraction>>.
* 2016-07-18 - Add examples of function-parameter and structure-member
  markup (based on public issue 286).
* 2016-07-11 - Change the document title.
* 2016-07-07 - Rename document, change license to CC BY, clarify required
  and recommended actions, and reserve use of "`normative`" for the
  Specifications.
* 2016-06-26 - Move Layers and Extensions chapter from Appendix C of the
  Vulkan API Specification and merge content with the naming guide.
  Put extension and naming chapters into their own source files.
* 2016-06-20 - Add API naming guide.
* 2016-05-22 - Add markup and image creation rules, after fixing missing
  figure captions for public issue 219.
* 2016-05-01 - Include feedback from public issues 120 and 190.
  Use consistent conventions for defining structures.
  Use American rather than British spelling conventions.
* 2016-03-12 - Recommend against "the value of".
* 2016-02-26 - Replace use of the "maynot{cl}" macro with "may{cl} not".
* 2016-02-16 - Place asciidoc conversion post-release.
* 2016-02-09 - Added quotation mark convention.
* 2016-02-01 - Add the Oxford Comma section and issue resolution.
* 2016-01-26 - Add bullet-list style description of command parameters.
* 2016-01-11 - Add "`Numbers in Text`" section from WSI work.
* 2015-12-16 - Make "`begin / end`" preferred terms to "`start / finish`".
* 2015-12-15 - Make "`implementation`" preferred term instead of "`system`".
* 2015-12-13 - Add tlink{cl}/tname{cl} macros for function pointer types.
* 2015-12-10 - Initial release for feedback.
