<p>Markdown supports two styles of headers, <ahref="http://docutils.sourceforge.net/mirror/setext.html">Setext</a> and <ahref="http://www.aaronsw.com/2002/atx/">atx</a>.</p>
<p>Setext-style headers are “underlined” using equal signs (for first-level
headers) and dashes (for second-level headers). For example:</p>
<pre><code>This is an H1
=============
This is an H2
-------------
</code></pre>
<p>Any number of underlining <code>=</code>’s or <code>-</code>’s will work.</p>
<p>Atx-style headers use 1-6 hash characters at the start of the line,
corresponding to header levels 1-6. For example:</p>
<pre><code># This is an H1
## This is an H2
###### This is an H6
</code></pre>
<p>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
<p>Link definitions are only used for creating links during Markdown
processing, and are stripped from your document in the HTML output.</p>
<p>Link definition names may constist of letters, numbers, spaces, and punctuation — but they are <em>not</em> case sensitive. E.g. these two links:</p>
<pre><code>[link text][a]
[link text][A]
</code></pre>
<p>are equivalent.</p>
<p>The <em>implicit link name</em> shortcut allows you to omit the name of the
link, in which case the link text itself is used as the name.
Just use an empty set of square brackets — e.g., to link the word
“Google” to the google.com web site, you could simply write:</p>
<pre><code>[Google][]
</code></pre>
<p>And then define the link:</p>
<pre><code>[Google]: http://google.com/
</code></pre>
<p>Because link names may contain spaces, this shortcut even works for
multiple words in the link text:</p>
<pre><code>Visit [Daring Fireball][] for more information.
or <a href="http://search.msn.com/" title="MSN Search">MSN</a>.</p>
</code></pre>
<p>For comparison, here is the same paragraph written using
Markdown’s inline link style:</p>
<pre><code>I get 10 times more traffic from [Google](http://google.com/ "Google")
than from [Yahoo](http://search.yahoo.com/ "Yahoo Search") or
[MSN](http://search.msn.com/ "MSN Search").
</code></pre>
<p>The point of reference-style links is not that they’re easier to
write. The point is that with reference-style links, your document
source is vastly more readable. Compare the above examples: using
reference-style links, the paragraph itself is only 81 characters
long; with inline-style links, it’s 176 characters; and as raw HTML,
it’s 234 characters. In the raw HTML, there’s more markup than there
is text.</p>
<p>With Markdown’s reference-style links, a source document much more
closely resembles the final output, as rendered in a browser. By
allowing you to move the markup-related metadata out of the paragraph,
you can add links without interrupting the narrative flow of your
prose.</p>
<h3id="em">Emphasis</h3>
<p>Markdown treats asterisks (<code>*</code>) and underscores (<code>_</code>) as indicators of
emphasis. Text wrapped with one <code>*</code> or <code>_</code> will be wrapped with an
HTML <code><em></code> tag; double <code>*</code>’s or <code>_</code>’s will be wrapped with an HTML
<code><strong></code> tag. E.g., this input:</p>
<pre><code>*single asterisks*
_single underscores_
**double asterisks**
__double underscores__
</code></pre>
<p>will produce:</p>
<pre><code><em>single asterisks</em>
<em>single underscores</em>
<strong>double asterisks</strong>
<strong>double underscores</strong>
</code></pre>
<p>You can use whichever style you prefer; the lone restriction is that
the same character must be used to open and close an emphasis span.</p>
<p>Emphasis can be used in the middle of a word:</p>
<pre><code>un*fucking*believable
</code></pre>
<p>But if you surround an <code>*</code> or <code>_</code> with spaces, it’ll be treated as a
literal asterisk or underscore.</p>
<p>To produce a literal asterisk or underscore at a position where it
would otherwise be used as an emphasis delimiter, you can backslash
escape it:</p>
<pre><code>\*this text is surrounded by literal asterisks\*
</code></pre>
<h3id="code">Code</h3>
<p>To indicate a span of code, wrap it with backtick quotes (<code>`</code>).
Unlike a pre-formatted code block, a code span indicates code within a
normal paragraph. For example:</p>
<pre><code>Use the `printf()` function.
</code></pre>
<p>will produce:</p>
<pre><code><p>Use the <code>printf()</code> function.</p>
</code></pre>
<p>To include a literal backtick character within a code span, you can
backslash escape it:</p>
<pre><code>`There is a literal backtick (\`) here.`
</code></pre>
<p>Or, if you prefer, you can use multiple backticks as the opening and
closing delimiters:</p>
<pre><code>``There is a literal backtick (`) here.``
</code></pre>
<p>Both of the previous two examples will produce this:</p>
<pre><code><p><code>There is a literal backtick (`) here.</code></p>
</code></pre>
<p>With a code span, ampersands and angle brackets are encoded as HTML
entities automatically, which makes it easy to include example HTML
tags. Markdown will turn this:</p>
<pre><code>Please don't use any `<blink>` tags.
</code></pre>
<p>into:</p>
<pre><code><p>Please don't use any <code>&lt;blink&gt;</code> tags.</p>
</code></pre>
<p>You can write this:</p>
<pre><code>`&#8212;` is the decimal-encoded equivalent of `&mdash;`.
</code></pre>
<p>to produce:</p>
<pre><code><p><code>&amp;#8212;</code> is the decimal-encoded
equivalent of <code>&amp;mdash;</code>.</p>
</code></pre>
<h3id="img">Images</h3>
<p>Admittedly, it’s fairly difficult to devise a “natural” syntax for
placing images into a plain text document format.</p>
<p>Markdown uses an image syntax that is intended to resemble the syntax
for links, allowing for two styles: <em>inline</em> and <em>reference</em>.</p>
<p>Inline image syntax looks like this:</p>
<pre><code>
</code></pre>
<p>That is:</p>
<ul>
<li>An exclamation mark: <code>!</code>;</li>
<li>followed by a set of square brackets, containing the <code>alt</code>
attribute text for the image;</li>
<li>followed by a set of parentheses, containing the URL or path to
the image, and an optional <code>title</code> attribute enclosed in double
or single quotes.</li>
</ul>
<p>Reference-style image syntax looks like this:</p>
<pre><code>![Alt text][id]
</code></pre>
<p>Where “id” is the name of a defined image reference. Image references
are defined using syntax identical to link references:</p>
<pre><code>[id]: url/to/image "Optional title attribute"
</code></pre>
<p>As of this writing, Markdown has no syntax for specifying the
dimensions of an image; if this is important to you, you can simply
use regular HTML <code><img></code> tags.</p>
<hr/>
<h2id="misc">Miscellaneous</h2>
<h3id="autolink">Automatic Links</h3>
<p>Markdown supports a shortcut style for creating “automatic” links for URLs and email addresses: simply surround the URL or email address with angle brackets. What this means is that if you want to show the actual text of a URL or email address, and also have it be a clickable link, you can do this:</p>
