<p><strong>Note:</strong> This document is itself written using Markdown; you
can <ahref="http://daringfireball.net/projects/markdown/syntax.text">see the source for it by adding '.text' to the URL</a>.</p>
<hr/>
<h2id="overview">Overview</h2>
<h3id="philosophy">Philosophy</h3>
<p>Markdown is intended to be as easy-to-read and easy-to-write as is feasible.</p>
<p>Markdown 將容易閱讀和容易寫作這兩點作為主要目標。</p>
<p>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 <ahref="http://docutils.sourceforge.net/mirror/setext.html">Setext</a>, <ahref="http://www.aaronsw.com/2002/atx/">atx</a>, <ahref="http://textism.com/tools/textile/">Textile</a>, <ahref="http://docutils.sourceforge.net/rst.html">reStructuredText</a>,
<ahref="http://www.triptico.com/software/grutatxt.html">Grutatext</a>, and <ahref="http://ettext.taint.org/doc/">EtText</a> -- the single biggest source of
inspiration for Markdown's syntax is the format of plain text email.</p>
<p>in your anchor tag <code>href</code> 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.</p>
<p>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 <code>&amp;</code>.</p>
<p>So, if you want to include a copyright symbol in your article, you can write:</p>
<pre><code>&copy;
</code></pre>
<p>and Markdown will leave it alone. But if you write:</p>
<pre><code>AT&T
</code></pre>
<p>Markdown will translate it to:</p>
<pre><code>AT&amp;T
</code></pre>
<p>Similarly, because Markdown supports <ahref="#html">inline HTML</a>, if you use
angle brackets as delimiters for HTML tags, Markdown will treat them as
such. But if you write:</p>
<pre><code>4 < 5
</code></pre>
<p>Markdown will translate it to:</p>
<pre><code>4 &lt; 5
</code></pre>
<p>However, inside Markdown code spans and blocks, angle brackets and
ampersands are <em>always</em> 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 <code><</code>
and <code>&</code> in your example code needs to be escaped.)</p>
<hr/>
<h2id="block">Block Elements</h2>
<h3id="p">Paragraphs and Line Breaks</h3>
<p>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.</p>
<p>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 <code><br /></code> tag.</p>
<p>When you <em>do</em> want to insert a <code><br /></code> break tag using Markdown, you
end a line with two or more spaces, then type return.</p>
<p>Yes, this takes a tad more effort to create a <code><br /></code>, but a simplistic
"every line break is a <code><br /></code>" rule wouldn't work for Markdown.
Markdown's email-style <ahref="#blockquote">blockquoting</a> and multi-paragraph <ahref="#list">list items</a>
work best -- and look better -- when you format them with hard breaks.</p>
<h3id="header">Headers</h3>
<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
determines the header level.) :</p>
<pre><code># This is an H1 #
## This is an H2 ##
### This is an H3 ######
</code></pre>
<h3id="blockquote">Blockquotes</h3>
<p>Markdown uses email-style <code>></code> 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 <code>></code> before every line:</p>
<pre><code>> 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.
</code></pre>
<p>Markdown allows you to be lazy and only put the <code>></code> before the first
line of a hard-wrapped paragraph:</p>
<pre><code>> 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.
</code></pre>
<p>Blockquotes can be nested (i.e. a blockquote-in-a-blockquote) by
adding additional levels of <code>></code>:</p>
<pre><code>> This is the first level of quoting.
>
>> This is nested blockquote.
>
> Back to the first level.
</code></pre>
<p>Blockquotes can contain other Markdown elements, including headers, lists,
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*frigging*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 use
multiple backticks as the opening and closing delimiters:</p>
<pre><code>``There is a literal backtick (`) here.``
</code></pre>
<p>which will produce this:</p>
<pre><code><p><code>There is a literal backtick (`) here.</code></p>
</code></pre>
<p>The backtick delimiters surrounding a code span may include spaces --
one after the opening, one before the closing. This allows you to place
literal backtick characters at the beginning or end of a code span:</p>
<pre><code>A single backtick in a code span: `` ` ``
A backtick-delimited string in a code span: `` `foo` ``
</code></pre>
<p>will produce:</p>
<pre><code><p>A single backtick in a code span: <code>`</code></p>
<p>A backtick-delimited string in a code span: <code>`foo`</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>
