Vulkan-Docs/doc/specs/vulkan/style/markup.txt

[[markup]]
= Markup Style

This chapter demonstrates Asciidoc and Specification structure, including
text layout and markup style.

Chapters and sections follow a rigid template consisting of an optional
anchor (if other parts of the document cross-reference the section) followed
by a one line title (see section 11.2 of the <<userguide,User Guide>>) and a
blank line. The anchor is typically the base name of the file containing the
chapter, with a lowercased version of the section name following, with
spaces replaced by dashes.

Always use the one-line title form, with one to five = signs preceding the
chapter/section title. The two-line title form cannot be easily searched for
and often looks like other types of asciidoc delimiters.

Always precede the anchor by two blank lines (except at the beginning of a
file), and follow the title by a blank line, to set off sections visibly.

.Example Markup
----
[[markup]]
= Markup Style


[[markup-sample-section]]
== Sample Section
----


[[markup-sample-section]]
== Sample Section

This is a sample section structurally similar to the <<Vulkan API
Specification>>, nested one
level inside a chapter. Sections can be nested up to level 5, although not
all levels are included in the Table of Contents.


[[markup-layout]]
== Layout, Line Lengths, and Lists

Asciidoc source should be text filled to 76 columns with hard line breaks.
Except when necessary for lists or other markup, text should begin at the
first column of each line (leading spaces are often semantically meaningful
in asciidoc markup).

UTF-8 characters outside the ASCII subset should be used sparingly, only
when needed for non-English names. Instead use asciidoc markup for special
characters, if required. For example, two hyphens produces an en-dash:

[NOTE]
.Example Markup
====

`An -- en-dash` -> An -- en-dash
====

As an exception, multiplication should be marked with the unicode
multiplication symbol ``×'' (and *not* an asterisk) when used in plain
text. In math sections, the same symbol should be referred to as `\times`.
In code sections, a conventional asterisk (`*`) should be used instead.

See chapter 10 of the <<userguide,User Guide>> for supported special
characters, as well as use of entity references.

Quotation marks should use the 66/99 convention. That is, double asymmetric
quotation marks, indicated by double back-ticks as opening marks and double
apostrophes as closing marks (\`\`like this''), which renders ``like this''.

_Never_ use hard tabs or trailing blanks.

* In some cases, limitations of asciidoc markup may result in lines that are
  longer than 76 characters and cannot easily be shortened without
  compromising the output documents.


[[markup-samplesection-lists]]
=== Lists

  * Bullet lists are the preferred form of list, aside from glossary
    definitions.
  * Lists should have text indented by 4 spaces and the list item delimiter
    (e.g. one or more asterisks, for bullet lists) indented by two spaces.
+
--
Note that continuation blocks for list items longer than one paragraph
cannot be indented, only the first paragraph.

In general, successive list items should not be separated by white space.
However, list continuation blocks must be followed by a blank line due to
limitations of the asciidoc parser.
--

  * Indent bullet lists two spaces (to the bullet), 4 spaces (to the text,
    if it extends over multiple lines). This lets us visually distinguish
    lists from other kinds of markup.
  ** Nested lists should align the leftmost list item delimiter (bullet,
     etc.) with the parent delimiter.

.Example Markup
----
  * This is the first item in a bullet list.
  * The second item is described with two paragraphs. The second
    paragraph is in a continuation block:
+
--
This is the second paragraph.
--

  ** This is a nested list item for the second item. Since it
     follows a continuation block, it must be separated by a
     blank line from that block.
----


[[markup-samplesection-anchors]]
=== Anchors and Cross-references

In general, chapters and sections should always have anchors, following the
naming convention <<markup,discussed above>>. Anchors to other sections of
the document may be inserted as needed. In addition, the autogenerated
include files defining commands, structures, enumerations and flags all
define anchors whose name is the name of the command or type being defined,
so it is easy to link to a (for example) a command name such as
<<vkCreateCommandPool>>.

If you want a cross-reference to an anchor to appear as something other than
the raw anchor name, always make sure to include that text as part of the
cross-reference. There are several different toolchains followed for various
forms of asciidoc output, and not all of them treat anchors without alt-text
the same way.

.Example Markup
----
In general, chapters and sections should always have anchors,
following the naming convention <<markup,discussed above>>.
Link to a command name such as <<vkCreateCommandPool>>.
----


[[markup-markup]]
== Markup Macros and Normative Terminology

This section discusses Asciidoc macros used in the document. In addition to
the macros defined by asciidoc itself, additional macros are defined by the
<<Vulkan API Specification>> and Reference Page configuration files.


[[markup-samplesection-images]]
=== Figures

All figures (images) must be marked up as follows, to ensure there is an
anchor and that the figure is given a caption which shows the figure number
and is added to the list of figures:

.Example Markup
----
[[fig-anchorname]]
image::images/imagename.{svgpdf}[align="center",title="Figure caption",{fullimagewidth}]
----

There must be both .svg and .pdf versions of each figure checked into the
+images/+ directory, to support generating both HTML and PDF outputs. It is
best to create images in Inkscape as SVG files and then use the conversion
rule in +images/Makefile+ to generate PDF.


=== API Markup Macros

These macros must be used to tag command, structure, enumeration,
enumerant, and other Vulkan-specific names so they can be rendered in a
distinctive fashion, link to definitions of those names, and be easily
searched for in the source documents. The validation scripts (`make
allchecks` output) also rely on these macros being used consistently and
correctly. The API markup macros, with examples of their use, are in the
following table:

.API Markup Macros
[width="100%",options="header",cols="20%,80%"]
|=====
| Macro Name    | Usage and Meaning
| flink{cl}     | Generates a cross-reference or link to the definition of
                  the command name in the macro argument. Example:
                  flink{cl}vkCreateCommandPool -> flink:vkCreateCommandPool.
| fname{cl}     | Formats the macro argument like flink{cl}. Does not
                  generate a cross-reference. Example:
                  fname{cl}vkCreateCommandPool -> fname:vkCreateCommandPool.
                  The flink{cl} macro is preferred.
| ftext{cl}     | Formats the macro argument like fname{cl}. May contain
                  asterisks for wildcards. Not validated. Example:
                  ftext{cl}vkCmd* -> ftext:vkCmd*.

                  Only use ftext{cl} when it is necessary to describe
                  something that should be rendered like a command name,
                  but is not actually one (e.g. is a wildcard or subset of
                  an actual command name).
| slink{cl}     | Generates a cross-reference or link to the definition
                  of the structure in the macro argument. Example:
                  slink{cl}VkCommandPoolCreateInfo ->
                  slink:VkCommandPoolCreateInfo.
| sname{cl}     | Formats the macro argument like slink{cl}. Does not
                  generate a cross-reference. May also be an abstract
                  structure or handle name. Example:
                  sname{cl}VkCommandPoolCreateInfo ->
                  sname:VkCommandPoolCreateInfo. The slink{cl} macro is
                  preferred if a definition of the target type with an
                  anchor exists in the document.
| stext{cl}     | Formats the macro argument like sname{cl}. May contain
                  asterisks for wildcards. Not validated. Example:
                  stext{cl}Vk*CreateInfo -> stext:Vk*CreateInfo.

                  Only use stext{cl} when it is necessary to describe
                  something that should be rendered like a structure name,
                  but is not actually one (e.g. is a wildcard or subset of
                  an actual structure name).
| elink{cl}     | Formats the macro argument as a Vulkan enumeration
                  name and links to the definition of that enumeration type.
                  Example: ename{cl}VkResult -> ename:VkResult.
| ename{cl}     | Formats the macro argument as a Vulkan enumerant name.
                  Example: ename{cl}VK_EVENT_SET -> ename:VK_EVENT_SET.
| etext{cl}     | Formats the macro argument like ename{cl}. Not validated.
                  Examples: etext{cl}_RANGE_SIZE -> etext:_RANGE_SIZE,
                  etext{cl}VK_IMAGE_CREATE_SPARSE_* ->
                  etext:VK_IMAGE_CREATE_SPARSE_*

                  Only use stext{cl} when it is necessary to describe
                  something that should be rendered like a enumerant name,
                  but is not actually one (e.g. is a wildcard or subset of
                  an actual enumerant name).
| pname{cl}     | Formats the macro argument as a Vulkan parameter or
                  structure member name. Example: pname{cl}device ->
                  pname:device.
| ptext{cl}     | Formats the macro argument like pname{cl}. May contain
                  asterisks for wildcards. Not validated. Example:
                  ptext{cl}sparseResidency* -> ptext:sparseResidency*.

                  Only use ptext{cl} when it is necessary to describe
                  something that should be rendered like a parameter name,
                  but is not actually one (e.g. is a wildcard or subset of
                  an actual parameter name).
| tlink{cl}     | Generates a cross-reference or link to the definition
                  of the Vulkan type in the macro argument. Example:
                  tlink{cl}PFN_vkAllocationFunction ->
                  tlink:PFN_vkAllocationFunction. This is only used for
                  function pointer types at present.
| tname{cl}     | Formats the macro argument like tlink{cl}. Does not
                  generate a cross-reference. Example:
                  tname{cl}PFN_vkAllocationFunction ->
                  tname:PFN_vkAllocationFunction. The tlink{cl} macro is
                  preferred.
| basetype{cl}  | Formats the macro argument like a basic scalar type
                  or API handle name. Not validated. Examples:
                  basetype{cl}uint32_t -> basetype:uint32_t,
                  basetype{cl}VkDeviceSize -> basetype:VkDeviceSize.
| code{cl}      | Formats the macro argument as a code sample. Primarily
                  used for SPIR-V keywords. Examples: code{cl}ClipDistance
                  -> code:ClipDistance, code{cl}VK_NULL_HANDLE ->
                  code:VK_NULL_HANDLE, code{cl}NULL -> code:NULL.
|=====


==== Other Markup

Uses of standard Asciidoc markup are less common. Occasional asterisk markup
is used for *emphasis*. Backtick markup is sometimes used for the C `NULL`
macro, but the code{cl} macro should be used for code:NULL instead.

.Example Markup
----
*emphasis*
`NULL`
code:NULL
----


==== Glossary Terms

_Glossary terms_ are currently marked up using underscore markup where they
are defined in the documents, as well as being added to the formal Glossary
appendix in the <<Vulkan API Specification>>. However, we will probably change to using
custom macros soon, to enable linkage between the glossary and definitions
in the spec body.

.Example Markup
----
_Glossary terms_
----


=== Normative Terminology

Normative terminology is precisely defined in section 1.3 of the
<<Vulkan API Specification>>, and is used to visually tag terms which express mandatory and
optional behavior of Vulkan implementations, and of applications using
Vulkan.

Whenever one of these terms appears in the <<Vulkan API Specification>>, it
must be tagged
using the macros, to indicate that its use has been carefully considered and
is consistent with the definitions in section 1.3. This is extremely
important for determining IP that is in and out of Scope during Ratification
reviews. The normative terminology macros are defined in the following
table:

.Normative Terminology Macros
[width="100%",options="header"]
|=====
| Macro Name     | Output
| can{cl}        | can:
| cannot{cl}     | cannot:
| may{cl}        | may:
| must{cl}       | must:
| mustnot{cl}    | mustnot:
| optional{cl}   | optional:
| optionally{cl} | optionally:
| recommend{cl}  | recommend:
| required{cl}   | required:
| should{cl}     | should:
| shouldnot{cl}  | shouldnot:
|=====

Because asciidoc macro names cannot contain spaces, macros which correspond
to multiple words (mustnot{cl}, and shouldnot{cl}) drop those spaces. Also
note that the macros are lower-case only, so language should be written such
that these terms do not appear at the beginning of a sentence (if really
necessary, additional capitalized macros could be added).


==== Optional Behavior

If a described behavior of the implementation is not necessary for
conformance, use the terms _may{cl}_ or _optional{cl}_ to describe it.

If a described usage pattern by the application is allowed but
not necessary, use the term _can{cl}_ to describe it.

If language flows more logically using the term "may not", use the term
_may{cl} not_ to describe it.


==== Optional Functionality

If functionality (rather than behavior) is optional, it should be
described as

.Example Markup
----
not required:
----

Implementations are not mandated to support functionality which is not
required, but if they do, they must behave as described by the
<<Vulkan API Specification>>. The term _functionality_ includes API features, extensions,
and layers.


[[markup-informative]]
== Informative, Editing and Implementor's Notes

There are several possible types of notes. Depending on the type of output,
they are rendered in different styles, but always include a note title, and
are usually set off in a box or with an icon. While asciidoc supports a wide
set of _admonition paragraphs_ such as TIP, IMPORTANT, WARNING, and CAUTION,
we always use the NOTE form, augmented by a note title. Each type of note is
discussed below.


[[markup-informative-notes]]
=== Informative Notes

Informative notes always appear as part of the document, but are considered
non-normative. They usually describe usage advice for applications, and are
always given the title _Note_, as in the following example:

[NOTE]
.Note
====
This is an informative note.
====

.Example Markup
----
[NOTE]
.Note
====
This is an informative note.
====
----

If an entire chapter or section is considered informative, it should begin
with the sentence:

.Example Markup
----
This chapter/section is Informative.
----


=== Editing Notes

Editing notes only appear in internal (non-published) versions of documents,
via asciidoc conditionals, and should be removed from the source before
pushing content to a canonical (master or per-extension) public repository.
They usually tag places where an outstanding bug or Gitlab/Github issue is
being worked, and are always given the title _editing-note_, as in the
following example:

ifdef::editing-notes[]
[NOTE]
.editing-note
====
This is an editing note, marked up as follows:
====
endif::editing-notes[]

.Example Markup
----
\ifdef::editing-notes[]
[NOTE]
.editing-note
====
Contents of an editing note go here. It is good practice to include a
bug/issue number, or link to the bug/issue, in the editing note.
====
\endif::editing-notes[]
----


=== Implementor's Notes

Implementor's notes may or may not appear in published versions of
documents, via asciidoc conditionals. They describe suggested approaches or
guidelines for people writing Vulkan implementations, and are rare because
the hardware being targeted varies so widely. They are always given the
title _Implementor's Note_, as in the following example:

ifdef::implementation-guide[]
.Implementor's Note
====
This is an implementor's note, marked up as follows:
====
endif::implementation-guide[]

.Example Markup
----
\ifdef::implementation-guide[]
.Implementor's Note
====
Contents of an implementor's note go here.
====
\endif::implementation-guide[]
----


== Word Choices

There are a variety of common terms that have several equivalent word
choices. Always use the words in the first column instead of the alternate
terms. This list may not be comprehensive; when in doubt, be guided by the
existing <<Vulkan API Specification>>.

.Word Choices
[width="100%",options="header"]
|=====
| Use This      | Instead Of     | Comments
| allocate      | create
                | When describing objects or memory resulting from
                  ftext:vkAllocate* commands.
| application   | client         |
| bitmask       | bitfield
                | Technically correct. Vulkan bitmasks are just integers and
                  are not logically addressable at the bit level.
| command       | function
                | Except when talking about function pointers returned by
                  ftext:vkGet*ProcAddr commands.
| create        | allocate
                | When describing objects resulting from ftext:vkCreate*
                  commands.
| depth/stencil | packed (interleaved, combined, _other prefix_)
                  depth/stencil, depth-stencil, DepthStencil, etc.
                | Combined format implicit in the name.
| device        | GPU
                | Implementations on non-GPU devices are possible.
| heterogeneous | heterogenous   | More common
| homogeneous   | homogenous     | More common
| host endianness | platform endianness |
| image subresource | subresource
                | Except when referring to *host-accessible subresources*
| implementation| system         |
| indices       | indexes        | More common
| member        | field          |
| pname:parameter are/is
                | pname:parameter specifies (denotes, indicates)
                | In rare cases when _are_ or _if_ are not grammatically
                  appropriate, _specifies_ may be used instead.
| pname:parameter is
                | the value of pname:parameter is
                | In rare cases, _the value of_ is appropriate. See the
                  existing specification language for examples.
| begins / begun      | starts / started | For ftext:vkBegin* - also see ``finish''
| finishes / finished | ends / ended     | For ftext:vkEnd* - also see ``begins''
| used          | referenced     | When describing attachments specified in a
                                   subpass description.
| statically used | referenced   | When describing resources or push constants
                                   accessed by shader code
| a more specific term | referenced | For all other situations.
| component     | channel        | Specifically this refers to color channels/components
|=====

[NOTE]
.Note
====
The ``begin/start'' and ``end/finish'' distinction is still being sorted out.
See Gitlab issue #61.
====


=== Avoid Contractions

Contractions make the specification sound less formal and using them would
be inconsistent with the many non-contraction forms already in use in the
spec.

.Word Choices
[width="100%",options="header"]
|=====
| Use This      | Instead Of
| are not       | aren't
| cannot{cl}    | can't
| does not      | doesn't
| do not        | don't
| has not       | hasn't
| is not        | isn't
| it is         | it's
| that is       | that's
| there is      | there's
| we are        | we're
| will not      | won't
|=====


=== Terms to Use With Caution

The term _subset_ is sometimes used to refer to a _strict subset_, and
sometimes used to refer to a subset which may be equal to the entire set.
This is particularly likely to come up when describing bitmasks. Make sure
to use either _subset_ or _strict subset_ as appropriate.

=== Terms to Avoid

Do not describe anything in the documentation using vague or wishy-washy
terms. Our goal is to precisely describe behavior of implementations.

The normative terms may{cl}, optional{cl}, and should{cl} are available when
implementations may make choices of behavior, but when such choices are
allowed, each choice still must have well-defined behavior.

.Terms to Avoid
[width="100%",options="header"]
|=====
| Bad Term | Comments
| expect   | And variants such as _expected_
| likely   | And variants such as _will likely_
| allowed, could, generally, might, probably, perhaps
           | And all other such terms of choice. Use _may{cl}_ or _can{cl}_
             depending on the context.
| may{cl} or may{cl} not   | Just use _may{cl}_.
|=====