CommonMark

A CommonMark-compliant parser for Julia.

Interface

using CommonMark

Create a markdown parser with the default CommonMark settings and then add footnote syntax to our parser.

parser = Parser()
enable!(parser, FootnoteRule())

Parse some text to an abstract syntax tree from a String:

ast = parser("Hello *world*")

Parse the contents of a source file:

ast = open(parser, "document.md")

Write ast to a string.

body = html(ast)
content = "<head></head><body>$body</body>"

Write to a file.

open("file.tex", "w") do file
    latex(file, ast)
    println(file, "rest of document...")
end

Or write to a buffer, such as stdout.

term(stdout, ast)

Output Formats

Supported output formats are currently:

html
latex
term: colourised and Unicode-formatted for display in a terminal.
markdown
notebook: Jupyter notebooks.

Extensions

Extensions can be enabled using the enable! function and disabled using disable!.

Typography

Convert ASCII dashes, ellipses, and quotes to their Unicode equivalents.

enable!(parser, TypographyRule())

Keyword arguments available for TypographyRule are

double_quotes
single_quotes
ellipses
dashes

which all default to true.

Admonitions

enable!(parser, AdmonitionRule())

Front matter

Fenced blocks at the start of a file containing structured data.

+++
[heading]
content = "..."
+++

The rest of the file...

The block must start on the first line of the file. Supported blocks are:

;;; for JSON
+++ for TOML
--- for YAML

To enable provide the FrontMatterRule with your choice of parsers for the formats:

using JSON
enable!(parser, FrontMatterRule(json=JSON.Parser.parse))

You can access front matter from a parsed file using frontmatter. As follows.

ast = open(parser, "document.md")
meta = frontmatter(ast)

Footnotes

enable!(parser, FootnoteRule())

Math

Julia-style inline and display maths:

Some ``\LaTeX`` math:

```math
f(a) = \frac{1}{2\pi}\int_{0}^{2\pi} (\alpha+R\cos(\theta))d\theta
```

Enabled with:

enable!(parser, MathRule())

Dollar-style inline and display math is also available using

enable!(parser, DollarMathRule())

Supported syntax:

single dollar signs surrounding inline math,
double dollars surrounding a single line paragraph for display math.

For more complex math, such as multiline display math, use the literal block syntax available with MathRule().

Tables

Pipe-style tables, similar to GitHub's tables. Literal | characters that are not wrapped in other syntax such as * must be escaped with a backslash. The number of columns in the table is specified by the second line.

| Column One | Column Two | Column Three |
|:---------- | ---------- |:------------:|
| Row `1`    | Column `2` |              |
| *Row* 2    | **Row** 2  | Column ``|`` |

Rows with more cells than specified have the trailing cells discarded, and rows with less cells are topped up with empty cells.

Enabled with:

enable!(parser, TableRule())

Raw Content

Overload literal syntax to support passing through any type of raw content.

enable!(parser, RawContentRule())

By default RawContentRule will handle inline and block content in HTML and LaTeX formats.

This is raw HTML: `<img src="myimage.jpg">`{=html}.

And here's an HTML block:

```{=html}
<div id="main">
 <div class="article">
```

```{=latex}
\begin{tikzpicture}
\draw[gray, thick] (-1,2) -- (2,-4);
\draw[gray, thick] (-1,-1) -- (2,2);
\filldraw[black] (0,0) circle (2pt) node[anchor=west] {Intersection point};
\end{tikzpicture}
```

This can be used to pass through different complex content that can't be easily handled by CommonMark natively without any loss of expressiveness.

Custom raw content handlers can also be passed through when enabling the rule. The naming scheme is <format>_inline or <format>_block.

enable!(p, RawContentRule(rst_inline=RstInline))

The last example would require the definition of a custom RstInline struct and associated display methods for all supported output types, namely: html, latex, and term. When passing your own keywords to RawContentRule the defaults are not included and must be enabled individually.

Attributes

Block and inline nodes can be tagged with arbitrary metadata in the form of key/value pairs using the AttributeRule extension.

enable!(p, AttributeRule())

Block attributes appear directly above the node that they target:

{#my_id color="red"}
# Heading

This will attach the metadata id="my_id" and color="red" to # Heading.

Inline attributes appear directly after the node that they target:

*Some styled text*{background="green"}.

Which will attach metadata background="green" to the emphasised text Some styled text.

CSS-style shorthand syntax #<name> and .<name> are available to use in place of id="<name>" and class="name". Multiple classes may be specified sequentially.

AttributeRule does not handle writing metadata to particular formats such as HTML or LaTeX. It is up to the implementation of a particular writer format to make use of available metadata itself. The built-in html and latex outputs make use of included attributes. html will include all provided attributes in the output, while latex makes use of only the #<id> attribute.

Citations

Use the following to enable in-text citations and reference list generation:

enable!(p, CitationRule())

Syntax for citations is similar to what is offered by Pandoc. Citations start with @.

Citations can either appear in square brackets [@id], or they can be written as
part of the text like @id. Bracketed citations can contain more than one
citation; separated by semi-colons [@one; @two; and @three].

{#refs}
# References

A reference section that will be populated with a list of all references can be marked using a {#refs} attribute from AttributeRule at the toplevel of the document. The list will be inserted after the node, in this case # References.

Citations and reference lists are formatted following the Chicago Manual of Style. Styling will, in future versions, be customisable using Citation Style Language styles.

The reference data used for citations must be provided in a format matching CSL JSON. Pass this data to CommonMark.jl when writing an AST to a output format.

html(ast, Dict{String,Any}("references" => JSON.parsefile("references.json")))

CSL JSON can be exported easily from reference management software such as Zotero or generated via pandoc-citeproc --bib2json or similar. The references data can be provided by the front matter section of a document so long as the FrontMatterRule has been enabled, though this does require writing your CSL data manually.

Note that the text format of the reference list is not important, and does not have to be JSON data. So long as the shape of the data matches CSL JSON it is valid. Below we use YAML references embedded in the document's front matter:

---
references:
- id: abelson1996
  author:
    - family: Abelson
      given: Harold
    - family: Sussman
      given: Gerald Jay
  edition: 2nd Editon
  event-place: Cambridge
  ISBN: 0-262-01153-0
  issued:
    date-parts:
      - - 1996
  publisher: MIT Press/McGraw-Hill
  publisher-place: Cambridge
  title: Structure and interpretation of computer programs
  type: book
---

Here's a citation [@abelson1996].

{#refs}
# References

Auto Identifiers

Headings within a document can be assigned ids automatically using

enable!(p, AutoIdentifierRule())

Identifiers are determined with CommonMark.slugify, which is based on the algorithm used by Pandoc. Non-unique identifiers are suffixed with a numeric counter and so cannot be considered stable. If you need stable identifiers then you should use AttributeRule to assign stable ids manually.

CommonMark Defaults

Block rules enabled by default in Parser objects:

AtxHeadingRule()
BlockQuoteRule()
FencedCodeBlockRule()
HtmlBlockRule()
IndentedCodeBlockRule()
ListItemRule()
SetextHeadingRule()
ThematicBreakRule()

Inline rules enabled by default in Parser objects:

AsteriskEmphasisRule()
AutolinkRule()
HtmlEntityRule()
HtmlInlineRule()
ImageRule()
InlineCodeRule()
LinkRule()
UnderscoreEmphasisRule()

These can all be disabled using disable!. Note that disabling some parser rules may result in unexpected results. It is recommended to be conservative in what is disabled.

Note

Until version 1.0.0 the rules listed above are subject to change and should be considered unstable regardless of whether they are exported or not.

Writer Configuration

When writing to an output format configuration data can be provided by:

passing a Dict{String,Any} to the writer method,
front matter in the source document using the FrontMatterRule extension.

Front matter takes precedence over the passed Dict.

Notable Variables

Values used to determine template behaviour:

template-engine::Function Used to render standalone document templates.

No default is provided by this package. The template-engine function should follow the interface provided by Mustache.render. It is recommended to use Mustache.jl to provide this functionalilty.

Syntax for opening and closing tags used by CommonMark.jl is ${...}. See the templates in src/writers/templates for usage examples.
<format>.template.file::String Custom template file to use for standalone <format>.
<format>.template.string::String Custom template string to use for standalone <format>.

Generic variables that can be included in templates to customise documents:

abstract::String Summary of the document.
authors::Vector{String} Vector of author names.
date::String Date of file generation.
keywords::Vector{String} Vector of keywords to be included in the document metadata.
lang::String Language of the document.
title::String Title of the document.
subtitle::String Subtitle of the document.

Format-specific variables that should be used only in a particular format's template. They are namespaced to avoid collision with other variables.

html
- html.css::Vector{String} Vector of CSS files to include in document.
- html.js::Vector{String} Vector of JavaScript files to include in document.
- html.header::String String content to add at end of <head>.
- html.footer::String String content to add at end of <body>.
latex
- latex.documentclass::String Class file to use for document. Default is article.
- latex.preamble::String String content to add directly before \begin{document}.

The following are automatically available in document templates.

body::String Main content of the page.
curdir::String Current directory.
outputfile::String Name of file that is being written to. When writing to an in-memory buffer this variable is not defined.

fonsp/CommonMark.jl