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Saturday December 5, 2020 By David Quintanilla
A Formal Specification For Markdown — Smashing Magazine


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Adebiyi Adedotun Lukman is a UI/Frontend Engineer primarily based in Lagos, Nigeria who additionally occurs to like UI/UX Design for the love of nice software program merchandise. When …
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Markdown is a strong markup language that enables enhancing and formatting in plain textual content format that may then be parsed and rendered as HTML. It has a declarative syntax that’s each highly effective and straightforward to study for technical and non-technical people. Nevertheless, because of the consequential ambiguities in its authentic specification, there have been various distinct flavors (or custom versions) that intention to erase these ambiguities in addition to lengthen the unique syntax help. This has led to a steep divergence from what may be parsed and what’s rendered. CommonMark goals to offer a standardized specification of Markdown that displays its real-world utilization.

CommonMark is a rationalized model of Markdown syntax with a spec whose objective is to take away the ambiguities and inconsistency surrounding the unique Markdown specification. It gives a standardized specification that defines the widespread syntax of the language together with a set of complete assessments to validate Markdown implementations in opposition to this specification.

GitHub makes use of Markdown because the markup language for its person content material.

“CommonMark is an formidable undertaking to formally specify the Markdown syntax utilized by many web sites on the web in a means that displays its real-world utilization […] It permits folks to proceed utilizing Markdown the identical means they at all times have whereas providing builders a complete specification and reference implementations to interoperate and show Markdown in a constant means between platforms.”

— “A Formal Spec For GitHub Flavored Markdown,” The GitHub Weblog

In 2012, GitHub proceeded to create its personal taste of Markdown — GitHub Flavored Markdown (GFM) — to fight the shortage of Markdown standardization, and lengthen the syntax to its wants. GFM was constructed on prime of Sundown, a parser particularly constructed by GitHub to resolve a few of the shortcomings of the prevailing Markdown parsers on the time. 5 years after, in 2017, it introduced the deprecation of Sunset in favor of CommonMark parsing and rendering library, cmark in A formal spec for GitHub Flavored Markdown.

Within the Common Questions part of Markdown and Visual Studio Code, it’s documented that Markdown in VSCode targets the CommonMark Markdown specification utilizing the markdown-it library, which in itself follows the CommonMark specification.

CommonMark has been extensively adopted and carried out (see the List of CommonMark Implementations) to be used in numerous languages like C (e.g cmark), C# (e.g CommonMark.NET), JavaScript (e.g markdown-it) and so on. That is excellent news as builders and authors are steadily transferring to a brand new frontier of been ready to make use of Markdown with a constant syntax, and a standardized specification.

A Brief Be aware On Markdown Parsers

Markdown parsers are on the coronary heart of changing Markdown textual content into HTML, straight or not directly.

Parsers like cmark and commonmark.js don’t convert Markdown to HTML straight, as a substitute, they convert it to an Abstract Syntax Tree (AST), after which render the AST as HTML, making the method extra granular and topic to manipulation. In between parsing — to AST — and rendering — to HTML — for instance, the Markdown textual content might be prolonged.

CommonMark’s Markdown Syntax Help

Projects or platforms that already implement the CommonMark specification because the baseline of their particular taste are sometimes superset of the strict subset of the CommonMark Markdown specification. For essentially the most a part of it, CommonMark has mitigated plenty of ambiguities by constructing a spec that’s constructed to be constructed on. GFM is a primary instance, whereas it helps each CommonMark syntax, it additionally extends it to fits its utilization.

CommonMark’s syntax help may be restricted at first, for instance, it has no help for this table syntax, however it is very important know that that is by design as this comment in this thread of dialog reveals: that the supported syntax is strict and mentioned to be the core syntax of the language itself — the identical specified by its creator, John Gruber in Markdown: Syntax.

On the time of writing, listed below are various supported syntax:

  1. Paragraphs and Line Breaks,
  2. Headers,
  3. Emphasis and Robust Emphasis,
  4. Horizontal Guidelines,
  5. Lists,
  6. Hyperlinks,
  7. Photos,
  8. Blockquotes,
  9. Code,
  10. Code Blocks.

To observe together with the examples, it’s suggested that you simply use the commonmark.js dingus editor to check out the syntax and get the rendered Preview, generated HTML, and AST.

Paragraphs And Line Breaks

In Markdown, paragraphs are steady traces of textual content separated by at the very least a clean line.

The next guidelines outline a paragraph:

  1. Markdown paragraphs are rendered in HTML because the Paragraph element, <p>.
  2. Totally different paragraphs are separated with a number of clean traces between them.
  3. For a line break, a paragraph needs to be post-fixed with two clean areas (or its tab equal), or a backslash ().
Syntax Rendered HTML
This can be a line of textual content <p>This can be a line of textual content</p>
This can be a line of textual content
And one other line of textual content
And one other however the
similar paragraph
<p>This can be a line of textual content
And one other line of textual content
And one other however the
similar paragraph</p>
This can be a paragraph

And one other paragraph

And one other

<p>This can be a paragraph</p>
<p>And one other paragraph</p>
<p>And one other</p>
Two areas after a line of textual content
Or a post-fixed backslash
Each means a line break
<p>Two areas after a line of textual content<br /><br>Or a post-fixed backslash<br /><br>Each means a line break</p>

Headings

Headings in Markdown represents one of many HTML Heading elements. There are two methods to outline headings:

  1. ATX heading.
  2. Setext heading.

The next guidelines outline ATX headings:

  1. Heading degree 1 (h1), by means of to heading degree 6, (h6) are supported.
  2. Atx-style headings are prefixed with the hash (#) image.
  3. There must be at the very least a clean house separating the textual content and the hash (#) image.
  4. The rely of hashes is equal to the cardinal variety of the heading. One hash is h1, two hashes, h2, 6 hashes, h6.
  5. Additionally it is doable to append an arbitrary variety of hash image(s) to headings, though this doesn’t trigger any impact (i.e. # Heading 1 #)
Syntax Rendered HTML
# Heading 1 <h1>Heading 1</h1>
## Heading 2 <h2>Heading 2</h2>
### Heading 3 <h3>Heading 3</h3>
#### Heading 4 <h4>Heading 4</h4>
##### Heading 5 <h5>Heading 5</h5>
###### Heading 6 <h6>Heading 6</h6>
## Heading 2 ## <h2>Heading 2</h2>

The next guidelines outline Setext headings:

  1. Solely Heading degree 1 (h1), and heading degree 2, (h2) are supported.
  2. Setext-style definition is finished with the equals (=) and sprint symbols respectively.
  3. With Setext, at the very least one equal or sprint image is required.
Syntax Rendered HTML
Heading 1
=
<h1>Heading 1</h1>
Heading 2
<h2>Heading 2</h2>

Emphasis And Robust Emphasis

Emphasis in Markdown can both be italics or daring (robust emphasis).

The next guidelines outline emphasis:

  1. Abnormal and robust emphasis are rendered in HTML because the Emphasis, <em>, and Strong, <strong> component, respectively.
  2. A textual content bounded by a single asterisk (*) or underscore (_ ) will probably be an emphasis.
  3. A textual content bounded by double asterisks or underscore will probably be a robust emphasis.
  4. The bounding symbols (asterisks or underscore) should match.
  5. There should be no house between the symbols and the enclosed textual content.
Syntax Rendered HTML
_Italic_ <em>Italic</em>
*Italic* <em>Italic</em>
__Bold__ <robust>Italic</robust>
**Daring** <robust>Italic</robust>

Horizontal Rule

A Horizontal rule, <hr/> is created with three or extra asterisks (*), hyphens (-), or underscores (_), on a brand new line. The symbols are separated by any variety of areas, or in no way.

Syntax Rendered HTML
*** <hr />
* * * <hr />
--- <hr />
- - - <hr />
___ <hr />
_ _ _ <hr />

Lists

Lists in Markdown are both a bullet (unordered) record or an ordered record.

The next guidelines outline an inventory:

  1. Bullet lists are rendered in HTML because the Unordered list element, <ul>.
  2. Ordered lists are rendered in HTML because the Ordered list element, <ol>.
  3. Bullet lists use asterisks, pluses, and hyphens as markers.
  4. Ordered lists use numbers adopted by intervals or closing parenthesis.
  5. The markers should be constant (you have to solely use the marker you start with for the remainder of the record objects definition).
Syntax Rendered HTML
* one
* two
* three
<ul>
<li>one</li>
<li>two</li>
<li>three</li>
</ul>
+ one
+ two
+ three
<ul>
<li>one</li>
<li>two</li>
<li>three</li>
</ul>
– one
– two
– three
<ul>
<li>one</li>
<li>two</li>
<li>three</li>
</ul>
– one
– two
+ three
<ul>
<li>one</li>
<li>two</li>
</ul>
<ul>
<li>three</li>
</ul>
1. one
2. two
3. three
<ol>
<li>one</li>
<li>two</li>
<li>three</li>
</ol>
1. three
2. 4
3. 5
<ol begin=”3″>
<li>three</li>
<li>4</li>
<li>5</li>
</ol>
1. one
100. two
3. three
<ol>
<li>one</li>
<li>two</li>
<li>three</li>
</ol>

Hyperlinks are supported with the inline and reference format.

The next guidelines outline a hyperlink:

  1. Hyperlinks are rendered because the HTML Anchor element, <a>.
  2. The inline format has the syntax: [value](URL "optional-title") with no house between the brackets.
  3. The reference format has the syntax: [value][id] for the reference, and [id]: href "optional-title" for the hyperlink label, separated with at the very least a line.
  4. The id is the Definition Identifier and will include letters, numbers, areas, and punctuation.
  5. Definition Identifiers aren’t case delicate.
  6. There’s additionally help for Computerized Hyperlinks, the place the URL is bounded by the lower than (<) and larger than (>) image, and displayed actually.
<!--Markdown-->
[Google](https://google.com “Google”)
<!--Rendered HTML-->
<a href="https://google.com" title="Google">Google</a>

<!--Markdown-->
[Google](https://google.com)
<!--Rendered HTML-->
<a href="https://google.com">Google</a>

<!--Markdown-->
[Article](/2020/09/comparing-styling-methods-next-js)
<!--Rendered HTML-->
<a href="http://smashingmagazine.com/2020/09/comparing-styling-methods-next-js">Evaluating Styling Strategies In Subsequent.js</a>

<!--Markdown-->
[Google][id]
<!--No less than a line should be in-between-->
<!--Rendered HTML-->

Rendered HTML: <a href="https://google.com" title="Google">Google</a>

<!--Markdown-->
<https://google.com>
<!--Rendered HTML-->
<a href="https://google.com">google.com</a>

<!--Markdown-->
<mark@google.com>
<!--Rendered HTML-->
<a href="mailto:mark@google.com">mark@google.com</a>

Photos

Photos in Markdown follows the inline and reference codecs for Hyperlinks.

The next guidelines outline photographs:

  1. Photos are rendered because the HTML image element, <img>.
  2. The inline format has the syntax: ![alt text](image-url "optional-title").
  3. The reference format has the syntax: ![alt text][id] for the reference, and [id]: image-url "optional-title" for the picture label. Each needs to be separated by at the very least a clean line.
  4. The picture title is optionally available, and the image-url may be relative.
<!--Markdown-->
![alt text](image-url "optional-title")
<!--Rendered HTML-->
<img src="https://smashingmagazine.com/2020/12/commonmark-formal-specification-markdown/image-url" alt="alt textual content" title="optional-title" />

<!--Markdown-->
![alt text][id]
<!--No less than a line should be in-between-->
<!--Markdown-->

<!--Rendered HTML-->
<img src="https://smashingmagazine.com/2020/12/commonmark-formal-specification-markdown/image-url" alt="alt textual content" title="optional-title" />

Blockquotes

The HTML Block Quotation element, <blockquote>, may be created by prefixing a brand new line with the larger than image (>).

<!--Markdown-->
> This can be a blockquote component
> You can begin each new line
> with the larger than image.
> That provides you larger management
> over what will probably be rendered.

<!--Rendered HTML-->
<blockquote>
<p>This can be a blockquote component
You can begin each new line
with the larger than image.
That provides you larger management
over what will probably be rendered.</p>
</blockquote>

Blockquotes may be nested:

<!--Markdown-->
> Blockquote with a paragraph
>> And one other paragraph
>>> And one other

<!--Rendered HTML-->
<blockquote>
<p>Blockquote with a paragraph</p>
<blockquote>
<p>And one other paragraph</p>
<blockquote>
<p>And one other</p>
</blockquote>
</blockquote>
</blockquote>

They will additionally include different Markdown parts, like headers, code, record objects, and so forth.

<!--Markdown-->
> Blockquote with a paragraph
> # Heading 1
> Heading 2
> -
> 1. One
> 2. Two

<!--Rendered HTML-->
<blockquote>
<p>Blockquote with a paragraph</p>
<h1>Heading 1</h1>
<h2>Heading 2</h2>
<ol>
<li>One</li>
<li>Two</li>
</ol>
</blockquote>

Code

The HTML Inline Code element, <code>, can also be supported. To create one, delimit the textual content with back-ticks (`), or double back-ticks if there must be a literal back-tick within the enclosing textual content.

<!--Markdown-->
`inline code snippet`
<!--Rendered HTML-->
<code>inline code snippet</code>

<!--Markdown-->
`<button kind="button">Click on Me</button>`
<!--Rendered HTML-->
<code><button kind="button">Click on Me</button></code>

<!--Markdown-->
`` There's an inline back-tick (`). ``
<!--Rendered HTML-->
<code>There's an inline back-tick (`).</code>

Code Blocks

The HTML Preformatted Text element, <pre>, can also be supported. This may be completed with at the very least three and an equal variety of bounding back-ticks (`), or tildes (~) — usually known as a code-fence, or a brand new line beginning indentation of at the very least 4 areas.

<!--Markdown-->
```
const dedupe = (array) => [...new Set(array)];
```
<!--Rendered HTML-->
<pre><code>const dedupe = (array) => [...new Set(array)];</code></pre>

<!--Markdown-->
    const dedupe = (array) => [...new Set(array)];
<!--Rendered HTML-->
<pre><code>const dedupe = (array) => [...new Set(array)];</code></pre>

Utilizing Inline HTML

Based on John Grubers authentic spec note on inline HTML, any markup that’s not coated by Markdown’s syntax, you merely use HTML itself, with The one restrictions are that block-level HTML parts — e.g. <div>, <desk>, <pre>, <p>, and so on. — should be separated from surrounding content material by clean traces, and the beginning and finish tags of the block shouldn’t be indented with tabs or areas.

Nevertheless, until you might be most likely one of many folks behind CommonMark itself, or thereabout, you almost certainly will probably be writing Markdown with a taste that’s already prolonged to deal with a lot of syntax not at the moment supported by CommonMark.

Going Ahead

CommonMark is a continuing work in progress with its spec last updated on April 6, 2019. There are a selection of common applications supporting it within the pool of Markdown tools. With the notice of CommonMark’s effort in direction of standardization, I believe it’s enough to conclude that in Markdown’s simplicity, is plenty of work occurring behind the scenes and that it’s a good factor for the CommonMark effort that the formal specification of GitHub Flavored Markdown is predicated on the specification.

The transfer in direction of the CommonMark standardization effort doesn’t forestall the creation of flavors to increase its supported syntax, and as CommonMark gears up for launch 1.0 with issues that must be resolved, there are some fascinating assets concerning the steady effort that you need to use to your perusal.

Sources

Smashing Editorial
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