Markdown
Overview
Philosophy
Markdown is intended to be as easy-to-read and easy-to-write as is feasible.
Readability, however, is emphasized above all else. A Markdown-formatted document should be publishable as-is, as plain text, without looking like it's been marked up with tags or formatting instructions. While Markdown's syntax has been influenced by several existing text-to-HTML filters – including [Setext] [1], [atx] [2], [Textile] [3], [reStructuredText] [4], [Grutatext] [5], and [EtText] [6] – the single biggest source of inspiration for Markdown's syntax is the format of plain text email.
[1]: http://docutils.sourceforge.net/mirror/setext.html [2]: http://www.aaronsw.com/2002/atx/ [3]: http://textism.com/tools/textile/ [4]: http://docutils.sourceforge.net/rst.html [5]: http://www.triptico.com/software/grutatxt.html [6]: http://ettext.taint.org/doc/
To this end, Markdown's syntax is comprised entirely of punctuation characters, which punctuation characters have been carefully chosen so as to look like what they mean. E.g., asterisks around a word actually look like *emphasis*. Markdown lists look like, well, lists. Even blockquotes look like quoted passages of text, assuming you've ever used email.
Inline HTML
Markdown's syntax is intended for one purpose: to be used as a format for writing for the web.
Markdown is not a replacement for HTML, or even close to it. Its syntax is very small, corresponding only to a very small subset of HTML tags. The idea is not to create a syntax that makes it easier to insert HTML tags. In my opinion, HTML tags are already easy to insert. The idea for Markdown is to make it easy to read, write, and edit prose. HTML is a publishing format; Markdown is a writing format. Thus, Markdown's formatting syntax only addresses issues that can be conveyed in plain text.
For any markup that is not covered by Markdown's syntax, you simply use HTML itself. There's no need to preface it or delimit it to indicate that you're switching from Markdown to HTML; you just use the tags.
The only restrictions are that block-level HTML elements – e.g. <div>
,
<table>
, <pre>
, <p>
, etc. – must be separated from surrounding
content by blank lines, and the start and end tags of the block should
not be indented with tabs or spaces. Markdown is smart enough not
to add extra (unwanted) <p>
tags around HTML block-level tags.
For example, to add an HTML table to a Markdown article:
This is a regular paragraph.
<table> <tr> <td>Foo</td> </tr> </table>
This is another regular paragraph.
Note that Markdown formatting syntax is not processed within block-level
HTML tags. E.g., you can't use Markdown-style *emphasis*
inside an
HTML block.
Span-level HTML tags – e.g. <span>
, <cite>
, or <del>
– can be
used anywhere in a Markdown paragraph, list item, or header. If you
want, you can even use HTML tags instead of Markdown formatting; e.g. if
you'd prefer to use HTML <a>
or <img>
tags instead of Markdown's
link or image syntax, go right ahead.
Unlike block-level HTML tags, Markdown syntax is processed within span-level tags.
Automatic Escaping for Special Characters
In HTML, there are two characters that demand special treatment: <
and &
. Left angle brackets are used to start tags; ampersands are
used to denote HTML entities. If you want to use them as literal
characters, you must escape them as entities, e.g. <
, and
&
.
Ampersands in particular are bedeviling for web writers. If you want to
write about 'AT&T', you need to write 'AT&T
'. You even need to
escape ampersands within URLs. Thus, if you want to link to:
http://images.google.com/images?num=30&q=larry+bird
you need to encode the URL as:
http://images.google.com/images?num=30&q=larry+bird
in your anchor tag href
attribute. Needless to say, this is easy to
forget, and is probably the single most common source of HTML validation
errors in otherwise well-marked-up web sites.
Markdown allows you to use these characters naturally, taking care of
all the necessary escaping for you. If you use an ampersand as part of
an HTML entity, it remains unchanged; otherwise it will be translated
into &
.
So, if you want to include a copyright symbol in your article, you can write:
©
and Markdown will leave it alone. But if you write:
AT&T
Markdown will translate it to:
AT&T
Similarly, because Markdown supports inline HTML, if you use angle brackets as delimiters for HTML tags, Markdown will treat them as such. But if you write:
4 < 5
Markdown will translate it to:
4 < 5
However, inside Markdown code spans and blocks, angle brackets and
ampersands are always encoded automatically. This makes it easy to use
Markdown to write about HTML code. (As opposed to raw HTML, which is a
terrible format for writing about HTML syntax, because every single <
and &
in your example code needs to be escaped.)
Block Elements
Paragraphs and Line Breaks
A paragraph is simply one or more consecutive lines of text, separated by one or more blank lines. (A blank line is any line that looks like a blank line – a line containing nothing but spaces or tabs is considered blank.) Normal paragraphs should not be indented with spaces or tabs.
The implication of the „one or more consecutive lines of text“ rule is
that Markdown supports „hard-wrapped“ text paragraphs. This differs
significantly from most other text-to-HTML formatters (including Movable
Type's „Convert Line Breaks“ option) which translate every line break
character in a paragraph into a <br />
tag.
When you do want to insert a <br />
break tag using Markdown, you
end a line with two or more spaces, then type return.
Yes, this takes a tad more effort to create a <br />
, but a simplistic
„every line break is a <br />
“ rule wouldn't work for Markdown.
Markdown's email-style [blockquoting][bq] and multi-paragraph [list items][l]
work best – and look better – when you format them with hard breaks.
[bq]: #blockquote [l]: #list
Headers
Markdown supports two styles of headers, [Setext] [1] and [atx] [2].
Setext-style headers are „underlined“ using equal signs (for first-level headers) and dashes (for second-level headers). For example:
This is an H1 ============= This is an H2 -------------
Any number of underlining =
's or -
's will work.
Atx-style headers use 1-6 hash characters at the start of the line, corresponding to header levels 1-6. For example:
# This is an H1 ## This is an H2 ###### This is an H6
Optionally, you may „close“ atx-style headers. This is purely cosmetic – you can use this if you think it looks better. The closing hashes don't even need to match the number of hashes used to open the header. (The number of opening hashes determines the header level.) :
# This is an H1 # ## This is an H2 ## ### This is an H3 ######
Blockquotes
Markdown uses email-style >
characters for blockquoting. If you're
familiar with quoting passages of text in an email message, then you
know how to create a blockquote in Markdown. It looks best if you hard
wrap the text and put a >
before every line:
> This is a blockquote with two paragraphs. Lorem ipsum dolor sit amet, > consectetuer adipiscing elit. Aliquam hendrerit mi posuere lectus. > Vestibulum enim wisi, viverra nec, fringilla in, laoreet vitae, risus. > > Donec sit amet nisl. Aliquam semper ipsum sit amet velit. Suspendisse > id sem consectetuer libero luctus adipiscing.
Markdown allows you to be lazy and only put the >
before the first
line of a hard-wrapped paragraph:
> This is a blockquote with two paragraphs. Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Aliquam hendrerit mi posuere lectus. Vestibulum enim wisi, viverra nec, fringilla in, laoreet vitae, risus. > Donec sit amet nisl. Aliquam semper ipsum sit amet velit. Suspendisse id sem consectetuer libero luctus adipiscing.
Blockquotes can be nested (i.e. a blockquote-in-a-blockquote) by
adding additional levels of >
:
> This is the first level of quoting. > > > This is nested blockquote. > > Back to the first level.
Blockquotes can contain other Markdown elements, including headers, lists, and code blocks:
> ## This is a header. > > 1. This is the first list item. > 2. This is the second list item. > > Here's some example code: > > return shell_exec("echo $input | $markdown_script");
Any decent text editor should make email-style quoting easy. For example, with BBEdit, you can make a selection and choose Increase Quote Level from the Text menu.
Lists
Markdown supports ordered (numbered) and unordered (bulleted) lists.
Unordered lists use asterisks, pluses, and hyphens – interchangably – as list markers:
* Red * Green * Blue
is equivalent to:
+ Red + Green + Blue
and:
- Red - Green - Blue
Ordered lists use numbers followed by periods:
1. Bird 2. McHale 3. Parish
It's important to note that the actual numbers you use to mark the list have no effect on the HTML output Markdown produces. The HTML Markdown produces from the above list is:
<ol> <li>Bird</li> <li>McHale</li> <li>Parish</li> </ol>
If you instead wrote the list in Markdown like this:
1. Bird 1. McHale 1. Parish
or even:
3. Bird 1. McHale 8. Parish
you'd get the exact same HTML output. The point is, if you want to, you can use ordinal numbers in your ordered Markdown lists, so that the numbers in your source match the numbers in your published HTML. But if you want to be lazy, you don't have to.
If you do use lazy list numbering, however, you should still start the list with the number 1. At some point in the future, Markdown may support starting ordered lists at an arbitrary number.
List markers typically start at the left margin, but may be indented by up to three spaces. List markers must be followed by one or more spaces or a tab.
To make lists look nice, you can wrap items with hanging indents:
* Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Aliquam hendrerit mi posuere lectus. Vestibulum enim wisi, viverra nec, fringilla in, laoreet vitae, risus. * Donec sit amet nisl. Aliquam semper ipsum sit amet velit. Suspendisse id sem consectetuer libero luctus adipiscing.
But if you want to be lazy, you don't have to:
* Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Aliquam hendrerit mi posuere lectus. Vestibulum enim wisi, viverra nec, fringilla in, laoreet vitae, risus. * Donec sit amet nisl. Aliquam semper ipsum sit amet velit. Suspendisse id sem consectetuer libero luctus adipiscing.
If list items are separated by blank lines, Markdown will wrap the
items in <p>
tags in the HTML output. For example, this input:
* Bird * Magic
will turn into:
<ul> <li>Bird</li> <li>Magic</li> </ul>
But this:
* Bird * Magic
will turn into:
<ul> <li><p>Bird</p></li> <li><p>Magic</p></li> </ul>
List items may consist of multiple paragraphs. Each subsequent paragraph in a list item must be intended by either 4 spaces or one tab:
1. This is a list item with two paragraphs. Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Aliquam hendrerit mi posuere lectus. Vestibulum enim wisi, viverra nec, fringilla in, laoreet vitae, risus. Donec sit amet nisl. Aliquam semper ipsum sit amet velit. 2. Suspendisse id sem consectetuer libero luctus adipiscing.
It looks nice if you indent every line of the subsequent paragraphs, but here again, Markdown will allow you to be lazy:
* This is a list item with two paragraphs. This is the second paragraph in the list item. You're only required to indent the first line. Lorem ipsum dolor sit amet, consectetuer adipiscing elit. * Another item in the same list.
To put a blockquote within a list item, the blockquote's >
delimiters need to be indented:
* A list item with a blockquote: > This is a blockquote > inside a list item.
To put a code block within a list item, the code block needs to be indented twice – 8 spaces or two tabs:
* A list item with a code block: <code goes here>
It's worth noting that it's possible to trigger an ordered list by accident, by writing something like this:
1986. What a great season.
In other words, a number-period-space sequence at the beginning of a line. To avoid this, you can backslash-escape the period:
1986\. What a great season.
Code Blocks
Pre-formatted code blocks are used for writing about programming or
markup source code. Rather than forming normal paragraphs, the lines
of a code block are interpreted literally. Markdown wraps a code block
in both <pre>
and <code>
tags.
To produce a code block in Markdown, simply indent every line of the block by at least 4 spaces or 1 tab. For example, given this input:
This is a normal paragraph: This is a code block.
Markdown will generate:
<p>This is a normal paragraph:</p> <pre><code>This is a code block. </code></pre>
One level of indentation – 4 spaces or 1 tab – is removed from each line of the code block. For example, this:
Here is an example of AppleScript: tell application "Foo" beep end tell
will turn into:
<p>Here is an example of AppleScript:</p> <pre><code>tell application "Foo" beep end tell </code></pre>
A code block continues until it reaches a line that is not indented (or the end of the article).
Within a code block, ampersands (&
) and angle brackets (<
and >
)
are automatically converted into HTML entities. This makes it very
easy to include example HTML source code using Markdown – just paste
it and indent it, and Markdown will handle the hassle of encoding the
ampersands and angle brackets. For example, this:
<div class="footer"> © 2004 Foo Corporation </div>
will turn into:
<pre><code><div class="footer"> &copy; 2004 Foo Corporation </div> </code></pre>
Regular Markdown syntax is not processed within code blocks. E.g., asterisks are just literal asterisks within a code block. This means it's also easy to use Markdown to write about Markdown's own syntax.
Horizontal Rules
You can produce a horizontal rule tag (<hr />
) by placing three or
more hyphens, asterisks, or underscores on a line by themselves. If you
wish, you may use spaces between the hyphens or asterisks. Each of the
following lines will produce a horizontal rule:
* * * *** ***** - - - ---------------------------------------
<h2 id=„span“
>Span Elements</h2>
<h3 id=„link“
>Links</h3>