# Nim-flavored Markdown and reStructuredText

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Author: | Andrey Makarov
Version: | 2.2.8

Both Markdown (md) and reStructuredText (RST) are markup languages whose goal is to typeset texts with complex structure, formatting and references using simple plaintext representation.

# Command line usage

Usage (to convert Markdown into HTML):

    nim md2html markdown_rst.md

Output:

    You're reading it!

The `md2tex` command is invoked identically to `md2html`, but outputs a `.tex` file instead of `.html`.

These tools embedded into Nim compiler; the compiler can output the result to HTML [1] or Latex [2].

[1]
commands `nim doc` for `*.nim` files and `nim rst2html` for `*.rst` files
[2]
commands `nim doc2tex` for `*.nim` and `nim rst2tex` for `*.rst`.

Full list of supported commands:

command | runs on... | input format | output format
--- | --- | --- | ---
`nim md2html` | standalone md files | `.md` | `.html` HTML
`nim md2tex` | same | same | `.tex` LaTeX
`nim rst2html` | standalone rst files | `.rst` | `.html` HTML
`nim rst2tex` | same | same | `.tex` LaTeX
`nim doc` | documentation comments | `.nim` | `.html` HTML
`nim doc2tex` | same | same | `.tex` LaTeX
`nim jsondoc` | same | same | `.json` JSON

# Basic markup

If you are new to Markdown/RST please consider reading the following:

1. Markdown Basic Syntax
2. a long specification of Markdown: CommonMark Spec
3. a short quick introduction to RST
4. an RST reference: a comprehensive cheatsheet for RST
5. a more formal 50-page RST specification.

## Features

A large subset is implemented with some limitations and additional Nim-specific features.

Supported common RST/Markdown features:

- body elements
  - sections
  - transitions
  - paragraphs
  - bullet lists using +, *, -
  - enumerated lists using arabic numerals or alphabet characters: 1. ... 2. ... or a. ... b. ... or A. ... B. ...
  - footnotes (including manually numbered, auto-numbered, auto-numbered with label, and auto-symbol footnotes) and citations
  - field lists
  - option lists
  - quoted literal blocks
  - line blocks
  - simple tables
  - directives (see official documentation in RST directives list):
    - `image`, `figure` for including images and videos
    - `code`
    - `contents` (table of contents), `container`, `raw`
    - `include`
    - admonitions: "attention", "caution", "danger", "error", "hint", "important", "note", "tip", "warning", "admonition"
    - substitution definitions: `replace` and `image`
  - comments
- inline markup
  - emphasis, strong emphasis, `inline literals`, hyperlink references (including embedded URI), substitution references, standalone hyperlinks, internal links (inline and outline)
  - `interpreted text` with roles `:literal:`, `:strong:`, `emphasis`, `:sub:`/`:subscript:`, `:sup:`/`:superscript:` (see RST roles list for description).
  - inline internal targets

## RST mode only features

- RST syntax for definition lists (that is additional indentation after a definition line)
- indented literal blocks starting from `::`

## Markdown-specific features

- Markdown tables
- Markdown code blocks. For them the same additional arguments as for RST code blocks can be provided (e.g. `test` or `number-lines`) but with a one-line syntax like this:

      ```nim test number-lines=10
      echo "ok"
      ```

- Markdown links `[...](...)`
- Pandoc syntax for automatic links `[...]`, see Referencing for description
- Pandoc syntax for footnotes, including `[^10]` (manually numbered) and `[^someName]` (auto-numbered with a label)
- Markdown literal blocks indented by 4 or more spaces
- Markdown headlines
- Markdown block quotes
- Markdown syntax for definition lists
- using `1` as auto-enumerator in enumerated lists like RST `#` (auto-enumerator `1` can not be used with `#` in the same list)

## Additional Nim-specific features

- referencing to definitions in external files, see Markup external referencing section
- directives: `code-block` [3], `title`, `index` [3]
- predefined roles
  - `:nim:` (default), `:c:` (C programming language), `:python:`, `:yaml:`, `:java:`, `:cpp:` (C++), `:csharp` (C#). That is every language that highlite supports. They turn on appropriate syntax highlighting in inline code.
    Note: default role for Nim files is `:nim:`, for `*.rst` it's currently `:literal:`.
  - generic command line highlighting roles:
    - `:cmd:` for commands and common shells syntax
    - `:console:` the same for interactive sessions (commands should be prepended by `$`)
    - `:program:` for executable names [3] (one can just use `:cmd:` on single word)
    - `:option:` for command line options [3]
  - `:tok:`, a role for highlighting of programming language tokens
- triple emphasis (bold and italic) using ***
- `:idx:` role for `interpreted text` to include the link to this text into an index (example: Nim index).
- double slash `//` in option lists serves as a prefix for any option that starts from a word (without any leading symbols like `-`, `--`, `/`):

      //compile   compile the project
      //doc       generate documentation

  Here the dummy `//` will disappear, while options `compile` and `doc` will be left in the final document.

- emoji / smiley symbols

[3]
similar but different from the directives of Python Sphinx directives and Sphinx roles extensions
Note: By default Nim has `roSupportMarkdown` and `roSupportRawDirective` turned on.
Warning: Using Nim-specific features can cause other Markdown and RST implementations to fail on your document.

# Referencing

To be able to copy and share links Nim generates anchors for all main document elements:

- headlines (including document title)
- footnotes
- explicitly set anchors: RST internal cross-references and inline internal targets
- Nim symbols (external referencing), see Nim DocGen Tools Guide for details.

But direct use of those anchors have 2 problems:

1. the anchors are usually mangled (e.g. spaces substituted to minus signs, etc).
2. manual usage of anchors is not checked, so it's easy to get broken links inside your project if e.g. spelling has changed for a heading or you use a wrong relative path to your document.

That's why Nim implementation has syntax for using original labels for referencing. Such referencing can be either local/internal or external:

- Local referencing (inside any given file) is defined by RST standard or Pandoc Markdown User guide.
- External (cross-document) referencing is a Nim-specific feature, though it's not really different from local referencing by its syntax.

## Markup local referencing

There are 2 syntax option available for referencing to objects inside any given file, e.g. for headlines:

    Markdown                  RST

    Some headline             Some headline
    =============             =============

    Ref. [Some headline]      Ref. `Some headline`_

## Markup external referencing

The syntax is the same as for local referencing, but the anchors are saved in `.idx` files, so one needs to generate them beforehand, and they should be loaded by an `.. importdoc::` directive. E.g. if we want to reference section "Some headline" in `file1.md` from `file2.md`, then `file2.md` may look like:

    .. importdoc:: file1.md

    Ref. [Some headline]

    nim md2html --index:only file1.md  # creates ``htmldocs/file1.idx``
    nim md2html file2.md               # creates ``htmldocs/file2.html``

To allow cross-references between any files in any order (especially, if circular references are present), it's strongly recommended to make a run for creating all the indexes first:

    nim md2html --index:only file1.md  # creates ``htmldocs/file1.idx``
    nim md2html --index:only file2.md  # creates ``htmldocs/file2.idx``
    nim md2html file1.md               # creates ``htmldocs/file1.html``
    nim md2html file2.md               # creates ``htmldocs/file2.html``

and then one can freely reference any objects as if these 2 documents are actually 1 file.

# Other

## Idiosyncrasies

Currently we do not aim at 100% Markdown or RST compatibility in inline markup recognition rules because that would provide very little user value. This parser has 2 modes for inline markup:

1. Markdown-like mode which is enabled by `roPreferMarkdown` option (turned on by default).
   Note: RST features like directives are still turned on
2. Compatibility mode which is RST rules.

Note: in both modes the parser interpretes text between single backticks (code) identically: backslash does not escape; the only exception: `\` folowed by ` does escape so that we can always input a single backtick ` in inline code. However that makes impossible to input code with `\` at the end in single backticks, one must use double backticks:

    `\`   -- WRONG
    ``\`` -- GOOD
    So single backticks can always be input: `\`` will turn to ` code

Attention: We don't support some obviously poor design choices of Markdown (or RST).

- no support for the rule of 2 spaces causing a line break in Markdown (use RST "line blocks" syntax for making line breaks)
- interpretation of Markdown block quotes is also slightly different, e.g. case

      >>> foo
      > bar
      >>baz

  is a single 3rd-level quote `foo bar baz` in original Markdown, while in Nim we naturally see it as 3rd-level quote `foo` + 1st level `bar` + 2nd level `baz`:

  > > > foo

  > bar

  > > baz

## Limitations

- no Unicode support in character width calculations
- body elements
  - no roman numerals in enumerated lists
  - no doctest blocks
  - no grid tables
  - some directives are missing (check official RST directives list): `parsed-literal`, `sidebar`, `topic`, `math`, `rubric`, `epigraph`, `highlights`, `pull-quote`, `compound`, `table`, `csv-table`, `list-table`, `section-numbering`, `header`, `footer`, `meta`, `class`
    - no `role` directives and no custom interpreted text roles
    - some standard roles are not supported (check RST roles list)
    - no generic admonition support
- inline markup
  - no simple-inline-markup
  - no embedded aliases

## Additional resources

- See Nim DocGen Tools Guide for the details about `nim doc` command and idiosyncrasies of documentation markup in `.nim` files and Nim programming language projects.
- See also documentation for rst module -- Nim RST/Markdown parser.