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Executable file
888 lines
27 KiB
Text
Executable file
Markdown: Syntax
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================
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<ul id="ProjectSubmenu">
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<li><a href="/projects/markdown/" title="Markdown Project Page">Main</a></li>
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<li><a href="/projects/markdown/basics" title="Markdown Basics">Basics</a></li>
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<li><a class="selected" title="Markdown Syntax Documentation">Syntax</a></li>
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<li><a href="/projects/markdown/license" title="Pricing and License Information">License</a></li>
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<li><a href="/projects/markdown/dingus" title="Online Markdown Web Form">Dingus</a></li>
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</ul>
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* [Overview](#overview)
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* [Philosophy](#philosophy)
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* [Inline HTML](#html)
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* [Automatic Escaping for Special Characters](#autoescape)
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* [Block Elements](#block)
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* [Paragraphs and Line Breaks](#p)
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* [Headers](#header)
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* [Blockquotes](#blockquote)
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* [Lists](#list)
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* [Code Blocks](#precode)
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* [Horizontal Rules](#hr)
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* [Span Elements](#span)
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* [Links](#link)
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* [Emphasis](#em)
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* [Code](#code)
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* [Images](#img)
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* [Miscellaneous](#misc)
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* [Backslash Escapes](#backslash)
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* [Automatic Links](#autolink)
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**Note:** This document is itself written using Markdown; you
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can [see the source for it by adding '.text' to the URL][src].
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[src]: /projects/markdown/syntax.text
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* * *
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<h2 id="overview">Overview</h2>
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<h3 id="philosophy">Philosophy</h3>
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Markdown is intended to be as easy-to-read and easy-to-write as is feasible.
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Readability, however, is emphasized above all else. A Markdown-formatted
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document should be publishable as-is, as plain text, without looking
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like it's been marked up with tags or formatting instructions. While
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Markdown's syntax has been influenced by several existing text-to-HTML
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filters -- including [Setext] [1], [atx] [2], [Textile] [3], [reStructuredText] [4],
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[Grutatext] [5], and [EtText] [6] -- the single biggest source of
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inspiration for Markdown's syntax is the format of plain text email.
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[1]: http://docutils.sourceforge.net/mirror/setext.html
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[2]: http://www.aaronsw.com/2002/atx/
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[3]: http://textism.com/tools/textile/
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[4]: http://docutils.sourceforge.net/rst.html
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[5]: http://www.triptico.com/software/grutatxt.html
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[6]: http://ettext.taint.org/doc/
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To this end, Markdown's syntax is comprised entirely of punctuation
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characters, which punctuation characters have been carefully chosen so
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as to look like what they mean. E.g., asterisks around a word actually
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look like \*emphasis\*. Markdown lists look like, well, lists. Even
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blockquotes look like quoted passages of text, assuming you've ever
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used email.
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<h3 id="html">Inline HTML</h3>
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Markdown's syntax is intended for one purpose: to be used as a
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format for *writing* for the web.
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Markdown is not a replacement for HTML, or even close to it. Its
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syntax is very small, corresponding only to a very small subset of
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HTML tags. The idea is *not* to create a syntax that makes it easier
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to insert HTML tags. In my opinion, HTML tags are already easy to
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insert. The idea for Markdown is to make it easy to read, write, and
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edit prose. HTML is a *publishing* format; Markdown is a *writing*
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format. Thus, Markdown's formatting syntax only addresses issues that
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can be conveyed in plain text.
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For any markup that is not covered by Markdown's syntax, you simply
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use HTML itself. There's no need to preface it or delimit it to
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indicate that you're switching from Markdown to HTML; you just use
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the tags.
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The only restrictions are that block-level HTML elements -- e.g. `<div>`,
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`<table>`, `<pre>`, `<p>`, etc. -- must be separated from surrounding
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content by blank lines, and the start and end tags of the block should
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not be indented with tabs or spaces. Markdown is smart enough not
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to add extra (unwanted) `<p>` tags around HTML block-level tags.
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For example, to add an HTML table to a Markdown article:
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This is a regular paragraph.
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<table>
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<tr>
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<td>Foo</td>
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</tr>
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</table>
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This is another regular paragraph.
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Note that Markdown formatting syntax is not processed within block-level
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HTML tags. E.g., you can't use Markdown-style `*emphasis*` inside an
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HTML block.
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Span-level HTML tags -- e.g. `<span>`, `<cite>`, or `<del>` -- can be
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used anywhere in a Markdown paragraph, list item, or header. If you
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want, you can even use HTML tags instead of Markdown formatting; e.g. if
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you'd prefer to use HTML `<a>` or `<img>` tags instead of Markdown's
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link or image syntax, go right ahead.
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Unlike block-level HTML tags, Markdown syntax *is* processed within
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span-level tags.
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<h3 id="autoescape">Automatic Escaping for Special Characters</h3>
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In HTML, there are two characters that demand special treatment: `<`
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and `&`. Left angle brackets are used to start tags; ampersands are
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used to denote HTML entities. If you want to use them as literal
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characters, you must escape them as entities, e.g. `<`, and
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`&`.
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Ampersands in particular are bedeviling for web writers. If you want to
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write about 'AT&T', you need to write '`AT&T`'. You even need to
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escape ampersands within URLs. Thus, if you want to link to:
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http://images.google.com/images?num=30&q=larry+bird
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you need to encode the URL as:
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http://images.google.com/images?num=30&q=larry+bird
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in your anchor tag `href` attribute. Needless to say, this is easy to
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forget, and is probably the single most common source of HTML validation
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errors in otherwise well-marked-up web sites.
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Markdown allows you to use these characters naturally, taking care of
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all the necessary escaping for you. If you use an ampersand as part of
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an HTML entity, it remains unchanged; otherwise it will be translated
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into `&`.
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So, if you want to include a copyright symbol in your article, you can write:
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©
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and Markdown will leave it alone. But if you write:
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AT&T
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Markdown will translate it to:
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AT&T
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Similarly, because Markdown supports [inline HTML](#html), if you use
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angle brackets as delimiters for HTML tags, Markdown will treat them as
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such. But if you write:
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4 < 5
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Markdown will translate it to:
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4 < 5
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However, inside Markdown code spans and blocks, angle brackets and
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ampersands are *always* encoded automatically. This makes it easy to use
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Markdown to write about HTML code. (As opposed to raw HTML, which is a
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terrible format for writing about HTML syntax, because every single `<`
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and `&` in your example code needs to be escaped.)
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* * *
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<h2 id="block">Block Elements</h2>
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<h3 id="p">Paragraphs and Line Breaks</h3>
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A paragraph is simply one or more consecutive lines of text, separated
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by one or more blank lines. (A blank line is any line that looks like a
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blank line -- a line containing nothing but spaces or tabs is considered
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blank.) Normal paragraphs should not be intended with spaces or tabs.
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The implication of the "one or more consecutive lines of text" rule is
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that Markdown supports "hard-wrapped" text paragraphs. This differs
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significantly from most other text-to-HTML formatters (including Movable
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Type's "Convert Line Breaks" option) which translate every line break
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character in a paragraph into a `<br />` tag.
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When you *do* want to insert a `<br />` break tag using Markdown, you
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end a line with two or more spaces, then type return.
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Yes, this takes a tad more effort to create a `<br />`, but a simplistic
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"every line break is a `<br />`" rule wouldn't work for Markdown.
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Markdown's email-style [blockquoting][bq] and multi-paragraph [list items][l]
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work best -- and look better -- when you format them with hard breaks.
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[bq]: #blockquote
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[l]: #list
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<h3 id="header">Headers</h3>
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Markdown supports two styles of headers, [Setext] [1] and [atx] [2].
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Setext-style headers are "underlined" using equal signs (for first-level
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headers) and dashes (for second-level headers). For example:
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This is an H1
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=============
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This is an H2
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-------------
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Any number of underlining `=`'s or `-`'s will work.
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Atx-style headers use 1-6 hash characters at the start of the line,
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corresponding to header levels 1-6. For example:
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# This is an H1
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## This is an H2
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###### This is an H6
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Optionally, you may "close" atx-style headers. This is purely
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cosmetic -- you can use this if you think it looks better. The
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closing hashes don't even need to match the number of hashes
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used to open the header. (The number of opening hashes
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determines the header level.) :
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# This is an H1 #
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## This is an H2 ##
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### This is an H3 ######
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<h3 id="blockquote">Blockquotes</h3>
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Markdown uses email-style `>` characters for blockquoting. If you're
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familiar with quoting passages of text in an email message, then you
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know how to create a blockquote in Markdown. It looks best if you hard
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wrap the text and put a `>` before every line:
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> This is a blockquote with two paragraphs. Lorem ipsum dolor sit amet,
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> consectetuer adipiscing elit. Aliquam hendrerit mi posuere lectus.
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> Vestibulum enim wisi, viverra nec, fringilla in, laoreet vitae, risus.
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>
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> Donec sit amet nisl. Aliquam semper ipsum sit amet velit. Suspendisse
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> id sem consectetuer libero luctus adipiscing.
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Markdown allows you to be lazy and only put the `>` before the first
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line of a hard-wrapped paragraph:
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> This is a blockquote with two paragraphs. Lorem ipsum dolor sit amet,
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consectetuer adipiscing elit. Aliquam hendrerit mi posuere lectus.
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Vestibulum enim wisi, viverra nec, fringilla in, laoreet vitae, risus.
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> Donec sit amet nisl. Aliquam semper ipsum sit amet velit. Suspendisse
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id sem consectetuer libero luctus adipiscing.
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Blockquotes can be nested (i.e. a blockquote-in-a-blockquote) by
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adding additional levels of `>`:
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> This is the first level of quoting.
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>
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> > This is nested blockquote.
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>
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> Back to the first level.
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Blockquotes can contain other Markdown elements, including headers, lists,
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and code blocks:
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> ## This is a header.
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>
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> 1. This is the first list item.
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> 2. This is the second list item.
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>
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> Here's some example code:
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>
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> return shell_exec("echo $input | $markdown_script");
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Any decent text editor should make email-style quoting easy. For
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example, with BBEdit, you can make a selection and choose Increase
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Quote Level from the Text menu.
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<h3 id="list">Lists</h3>
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Markdown supports ordered (numbered) and unordered (bulleted) lists.
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Unordered lists use asterisks, pluses, and hyphens -- interchangably
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-- as list markers:
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* Red
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* Green
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* Blue
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is equivalent to:
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+ Red
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+ Green
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+ Blue
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and:
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- Red
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- Green
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- Blue
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Ordered lists use numbers followed by periods:
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1. Bird
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2. McHale
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3. Parish
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It's important to note that the actual numbers you use to mark the
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list have no effect on the HTML output Markdown produces. The HTML
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Markdown produces from the above list is:
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<ol>
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<li>Bird</li>
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<li>McHale</li>
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<li>Parish</li>
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</ol>
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If you instead wrote the list in Markdown like this:
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1. Bird
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1. McHale
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1. Parish
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or even:
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3. Bird
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1. McHale
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8. Parish
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you'd get the exact same HTML output. The point is, if you want to,
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you can use ordinal numbers in your ordered Markdown lists, so that
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the numbers in your source match the numbers in your published HTML.
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But if you want to be lazy, you don't have to.
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If you do use lazy list numbering, however, you should still start the
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list with the number 1. At some point in the future, Markdown may support
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starting ordered lists at an arbitrary number.
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List markers typically start at the left margin, but may be indented by
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up to three spaces. List markers must be followed by one or more spaces
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or a tab.
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To make lists look nice, you can wrap items with hanging indents:
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* Lorem ipsum dolor sit amet, consectetuer adipiscing elit.
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Aliquam hendrerit mi posuere lectus. Vestibulum enim wisi,
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viverra nec, fringilla in, laoreet vitae, risus.
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* Donec sit amet nisl. Aliquam semper ipsum sit amet velit.
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Suspendisse id sem consectetuer libero luctus adipiscing.
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But if you want to be lazy, you don't have to:
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* Lorem ipsum dolor sit amet, consectetuer adipiscing elit.
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Aliquam hendrerit mi posuere lectus. Vestibulum enim wisi,
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viverra nec, fringilla in, laoreet vitae, risus.
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* Donec sit amet nisl. Aliquam semper ipsum sit amet velit.
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Suspendisse id sem consectetuer libero luctus adipiscing.
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If list items are separated by blank lines, Markdown will wrap the
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items in `<p>` tags in the HTML output. For example, this input:
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* Bird
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* Magic
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will turn into:
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<ul>
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<li>Bird</li>
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<li>Magic</li>
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</ul>
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But this:
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* Bird
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* Magic
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will turn into:
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<ul>
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<li><p>Bird</p></li>
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<li><p>Magic</p></li>
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</ul>
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List items may consist of multiple paragraphs. Each subsequent
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paragraph in a list item must be intended by either 4 spaces
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or one tab:
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1. This is a list item with two paragraphs. Lorem ipsum dolor
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sit amet, consectetuer adipiscing elit. Aliquam hendrerit
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mi posuere lectus.
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Vestibulum enim wisi, viverra nec, fringilla in, laoreet
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vitae, risus. Donec sit amet nisl. Aliquam semper ipsum
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sit amet velit.
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2. Suspendisse id sem consectetuer libero luctus adipiscing.
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It looks nice if you indent every line of the subsequent
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paragraphs, but here again, Markdown will allow you to be
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lazy:
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* This is a list item with two paragraphs.
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This is the second paragraph in the list item. You're
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only required to indent the first line. Lorem ipsum dolor
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sit amet, consectetuer adipiscing elit.
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* Another item in the same list.
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To put a blockquote within a list item, the blockquote's `>`
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delimiters need to be indented:
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* A list item with a blockquote:
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> This is a blockquote
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> inside a list item.
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To put a code block within a list item, the code block needs
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to be indented *twice* -- 8 spaces or two tabs:
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* A list item with a code block:
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<code goes here>
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It's worth noting that it's possible to trigger an ordered list by
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accident, by writing something like this:
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1986. What a great season.
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In other words, a *number-period-space* sequence at the beginning of a
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line. To avoid this, you can backslash-escape the period:
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1986\. What a great season.
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<h3 id="precode">Code Blocks</h3>
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Pre-formatted code blocks are used for writing about programming or
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markup source code. Rather than forming normal paragraphs, the lines
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of a code block are interpreted literally. Markdown wraps a code block
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in both `<pre>` and `<code>` tags.
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To produce a code block in Markdown, simply indent every line of the
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block by at least 4 spaces or 1 tab. For example, given this input:
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This is a normal paragraph:
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This is a code block.
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Markdown will generate:
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<p>This is a normal paragraph:</p>
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<pre><code>This is a code block.
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</code></pre>
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One level of indentation -- 4 spaces or 1 tab -- is removed from each
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line of the code block. For example, this:
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Here is an example of AppleScript:
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tell application "Foo"
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beep
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end tell
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will turn into:
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<p>Here is an example of AppleScript:</p>
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<pre><code>tell application "Foo"
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beep
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end tell
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</code></pre>
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A code block continues until it reaches a line that is not indented
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(or the end of the article).
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Within a code block, ampersands (`&`) and angle brackets (`<` and `>`)
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are automatically converted into HTML entities. This makes it very
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easy to include example HTML source code using Markdown -- just paste
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it and indent it, and Markdown will handle the hassle of encoding the
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ampersands and angle brackets. For example, this:
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<div class="footer">
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© 2004 Foo Corporation
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</div>
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will turn into:
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<pre><code><div class="footer">
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&copy; 2004 Foo Corporation
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</div>
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</code></pre>
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Regular Markdown syntax is not processed within code blocks. E.g.,
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asterisks are just literal asterisks within a code block. This means
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it's also easy to use Markdown to write about Markdown's own syntax.
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<h3 id="hr">Horizontal Rules</h3>
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You can produce a horizontal rule tag (`<hr />`) by placing three or
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more hyphens, asterisks, or underscores on a line by themselves. If you
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wish, you may use spaces between the hyphens or asterisks. Each of the
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following lines will produce a horizontal rule:
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* * *
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***
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*****
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- - -
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---------------------------------------
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_ _ _
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* * *
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<h2 id="span">Span Elements</h2>
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<h3 id="link">Links</h3>
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Markdown supports two style of links: *inline* and *reference*.
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In both styles, the link text is delimited by [square brackets].
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To create an inline link, use a set of regular parentheses immediately
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after the link text's closing square bracket. Inside the parentheses,
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put the URL where you want the link to point, along with an *optional*
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title for the link, surrounded in quotes. For example:
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This is [an example](http://example.com/ "Title") inline link.
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[This link](http://example.net/) has no title attribute.
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Will produce:
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<p>This is <a href="http://example.com/" title="Title">
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an example</a> inline link.</p>
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<p><a href="http://example.net/">This link</a> has no
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title attribute.</p>
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If you're referring to a local resource on the same server, you can
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use relative paths:
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See my [About](/about/) page for details.
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Reference-style links use a second set of square brackets, inside
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which you place a label of your choosing to identify the link:
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This is [an example][id] reference-style link.
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You can optionally use a space to separate the sets of brackets:
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This is [an example] [id] reference-style link.
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Then, anywhere in the document, you define your link label like this,
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on a line by itself:
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[id]: http://example.com/ "Optional Title Here"
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That is:
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* Square brackets containing the link identifier (optionally
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indented from the left margin using up to three spaces);
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* followed by a colon;
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* followed by one or more spaces (or tabs);
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* followed by the URL for the link;
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* optionally followed by a title attribute for the link, enclosed
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in double or single quotes.
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The link URL may, optionally, be surrounded by angle brackets:
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[id]: <http://example.com/> "Optional Title Here"
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You can put the title attribute on the next line and use extra spaces
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or tabs for padding, which tends to look better with longer URLs:
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[id]: http://example.com/longish/path/to/resource/here
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"Optional Title Here"
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Link definitions are only used for creating links during Markdown
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processing, and are stripped from your document in the HTML output.
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Link definition names may constist of letters, numbers, spaces, and punctuation -- but they are *not* case sensitive. E.g. these two links:
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[link text][a]
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[link text][A]
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are equivalent.
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The *implicit link name* shortcut allows you to omit the name of the
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link, in which case the link text itself is used as the name.
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Just use an empty set of square brackets -- e.g., to link the word
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"Google" to the google.com web site, you could simply write:
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[Google][]
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And then define the link:
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[Google]: http://google.com/
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Because link names may contain spaces, this shortcut even works for
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multiple words in the link text:
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Visit [Daring Fireball][] for more information.
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And then define the link:
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[Daring Fireball]: http://daringfireball.net/
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Link definitions can be placed anywhere in your Markdown document. I
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tend to put them immediately after each paragraph in which they're
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used, but if you want, you can put them all at the end of your
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document, sort of like footnotes.
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Here's an example of reference links in action:
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I get 10 times more traffic from [Google] [1] than from
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[Yahoo] [2] or [MSN] [3].
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[1]: http://google.com/ "Google"
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[2]: http://search.yahoo.com/ "Yahoo Search"
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[3]: http://search.msn.com/ "MSN Search"
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Using the implicit link name shortcut, you could instead write:
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I get 10 times more traffic from [Google][] than from
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[Yahoo][] or [MSN][].
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[google]: http://google.com/ "Google"
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[yahoo]: http://search.yahoo.com/ "Yahoo Search"
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[msn]: http://search.msn.com/ "MSN Search"
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Both of the above examples will produce the following HTML output:
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<p>I get 10 times more traffic from <a href="http://google.com/"
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title="Google">Google</a> than from
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<a href="http://search.yahoo.com/" title="Yahoo Search">Yahoo</a>
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or <a href="http://search.msn.com/" title="MSN Search">MSN</a>.</p>
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For comparison, here is the same paragraph written using
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Markdown's inline link style:
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I get 10 times more traffic from [Google](http://google.com/ "Google")
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than from [Yahoo](http://search.yahoo.com/ "Yahoo Search") or
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[MSN](http://search.msn.com/ "MSN Search").
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The point of reference-style links is not that they're easier to
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write. The point is that with reference-style links, your document
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source is vastly more readable. Compare the above examples: using
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reference-style links, the paragraph itself is only 81 characters
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long; with inline-style links, it's 176 characters; and as raw HTML,
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it's 234 characters. In the raw HTML, there's more markup than there
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is text.
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With Markdown's reference-style links, a source document much more
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closely resembles the final output, as rendered in a browser. By
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allowing you to move the markup-related metadata out of the paragraph,
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you can add links without interrupting the narrative flow of your
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prose.
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<h3 id="em">Emphasis</h3>
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Markdown treats asterisks (`*`) and underscores (`_`) as indicators of
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emphasis. Text wrapped with one `*` or `_` will be wrapped with an
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HTML `<em>` tag; double `*`'s or `_`'s will be wrapped with an HTML
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`<strong>` tag. E.g., this input:
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*single asterisks*
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_single underscores_
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**double asterisks**
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__double underscores__
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will produce:
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<em>single asterisks</em>
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<em>single underscores</em>
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<strong>double asterisks</strong>
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<strong>double underscores</strong>
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You can use whichever style you prefer; the lone restriction is that
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the same character must be used to open and close an emphasis span.
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Emphasis can be used in the middle of a word:
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un*fucking*believable
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But if you surround an `*` or `_` with spaces, it'll be treated as a
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literal asterisk or underscore.
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To produce a literal asterisk or underscore at a position where it
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would otherwise be used as an emphasis delimiter, you can backslash
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escape it:
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\*this text is surrounded by literal asterisks\*
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<h3 id="code">Code</h3>
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To indicate a span of code, wrap it with backtick quotes (`` ` ``).
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Unlike a pre-formatted code block, a code span indicates code within a
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normal paragraph. For example:
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Use the `printf()` function.
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will produce:
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<p>Use the <code>printf()</code> function.</p>
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To include a literal backtick character within a code span, you can use
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multiple backticks as the opening and closing delimiters:
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``There is a literal backtick (`) here.``
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which will produce this:
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<p><code>There is a literal backtick (`) here.</code></p>
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The backtick delimiters surrounding a code span may include spaces --
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one after the opening, one before the closing. This allows you to place
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literal backtick characters at the beginning or end of a code span:
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A single backtick in a code span: `` ` ``
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A backtick-delimited string in a code span: `` `foo` ``
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will produce:
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<p>A single backtick in a code span: <code>`</code></p>
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<p>A backtick-delimited string in a code span: <code>`foo`</code></p>
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With a code span, ampersands and angle brackets are encoded as HTML
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entities automatically, which makes it easy to include example HTML
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tags. Markdown will turn this:
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Please don't use any `<blink>` tags.
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into:
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<p>Please don't use any <code><blink></code> tags.</p>
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You can write this:
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`—` is the decimal-encoded equivalent of `—`.
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to produce:
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<p><code>&#8212;</code> is the decimal-encoded
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equivalent of <code>&mdash;</code>.</p>
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<h3 id="img">Images</h3>
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Admittedly, it's fairly difficult to devise a "natural" syntax for
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placing images into a plain text document format.
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Markdown uses an image syntax that is intended to resemble the syntax
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for links, allowing for two styles: *inline* and *reference*.
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Inline image syntax looks like this:
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That is:
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* An exclamation mark: `!`;
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* followed by a set of square brackets, containing the `alt`
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attribute text for the image;
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* followed by a set of parentheses, containing the URL or path to
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the image, and an optional `title` attribute enclosed in double
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or single quotes.
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Reference-style image syntax looks like this:
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![Alt text][id]
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Where "id" is the name of a defined image reference. Image references
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are defined using syntax identical to link references:
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[id]: url/to/image "Optional title attribute"
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As of this writing, Markdown has no syntax for specifying the
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dimensions of an image; if this is important to you, you can simply
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use regular HTML `<img>` tags.
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* * *
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<h2 id="misc">Miscellaneous</h2>
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<h3 id="autolink">Automatic Links</h3>
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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:
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<http://example.com/>
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Markdown will turn this into:
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<a href="http://example.com/">http://example.com/</a>
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Automatic links for email addresses work similarly, except that
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Markdown will also perform a bit of randomized decimal and hex
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entity-encoding to help obscure your address from address-harvesting
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spambots. For example, Markdown will turn this:
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<address@example.com>
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into something like this:
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<a href="mailto:addre
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ss@example.co
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m">address@exa
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mple.com</a>
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which will render in a browser as a clickable link to "address@example.com".
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(This sort of entity-encoding trick will indeed fool many, if not
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most, address-harvesting bots, but it definitely won't fool all of
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them. It's better than nothing, but an address published in this way
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will probably eventually start receiving spam.)
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<h3 id="backslash">Backslash Escapes</h3>
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Markdown allows you to use backslash escapes to generate literal
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characters which would otherwise have special meaning in Markdown's
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formatting syntax. For example, if you wanted to surround a word with
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literal asterisks (instead of an HTML `<em>` tag), you can backslashes
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before the asterisks, like this:
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\*literal asterisks\*
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Markdown provides backslash escapes for the following characters:
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\ backslash
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` backtick
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* asterisk
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_ underscore
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{} curly braces
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[] square brackets
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() parentheses
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# hash mark
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+ plus sign
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- minus sign (hyphen)
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. dot
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! exclamation mark
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