Autolinks

Autolink (opens new window)s are absolute URIs and email addresses inside < and >. They are parsed as links, with the URL or email address as the link label.
A URI autolink (opens new window) consists of <, followed by an absolute URI (opens new window) followed by >. It is parsed as a link to the URI, with the URI as the link’s label.
An absolute URI (opens new window), for these purposes, consists of a scheme (opens new window) followed by a colon (:) followed by zero or more characters other than ASCII whitespace (opens new window) and control characters, <, and >. If the URI includes these characters, they must be percent-encoded (e.g. %20 for a space).
For purposes of this spec, a scheme (opens new window) is any sequence of 2–32 characters beginning with an ASCII letter and followed by any combination of ASCII letters, digits, or the symbols plus (”+”), period (”.”), or hyphen (”-”).
Here are some valid autolinks:

Example 602

Markdown	HTML	Demo
<http://foo.bar.baz>	<p><a href="http://foo.bar.baz">http://foo.bar.baz</a></p>

Example 603

Markdown	HTML	Demo
<http://foo.bar.baz/test?q=hello&id=22&boolean>	<p><a href="http://foo.bar.baz/test?q=hello&amp;id=22&amp;boolean">http://foo.bar.baz/test?q=hello&amp;id=22&amp;boolean</a></p>

Example 604

Markdown	HTML	Demo
<irc://foo.bar:2233/baz>	<p><a href="irc://foo.bar:2233/baz">irc://foo.bar:2233/baz</a></p>

Uppercase is also fine:

Example 605

Markdown	HTML	Demo
<MAILTO:FOO@BAR.BAZ>	<p><a href="MAILTO:FOO@BAR.BAZ">MAILTO:FOO@BAR.BAZ</a></p>

Note that many strings that count as absolute URIs (opens new window) for purposes of this spec are not valid URIs, because their schemes are not registered or because of other problems with their syntax:

Example 606

Markdown	HTML	Demo
<a+b+c:d>	<p><a href="a+b+c:d">a+b+c:d</a></p>

Example 607

Markdown	HTML	Demo
<made-up-scheme://foo,bar>	<p><a href="made-up-scheme://foo,bar">made-up-scheme://foo,bar</a></p>

Example 608

Markdown	HTML	Demo
<http://../>	<p><a href="http://../">http://../</a></p>

Example 609

Markdown	HTML	Demo
<localhost:5001/foo>	<p><a href="localhost:5001/foo">localhost:5001/foo</a></p>

Spaces are not allowed in autolinks:

Example 610

Markdown	HTML	Demo
<http://foo.bar/baz bim>	<p>&lt;http://foo.bar/baz bim&gt;</p>

Backslash-escapes do not work inside autolinks:

Example 611

Markdown	HTML	Demo
<http://example.com/\[\>	<p><a href="http://example.com/%5C%5B%5C">http://example.com/\[\</a></p>

An email autolink (opens new window) consists of <, followed by an email address (opens new window), followed by >. The link’s label is the email address, and the URL is mailto: followed by the email address.
An email address (opens new window), for these purposes, is anything that matches the non-normative regex from the HTML5 spec (opens new window):

/^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?
(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/

Examples of email autolinks:

Example 612

Markdown	HTML	Demo
<foo@bar.example.com>	<p><a href="mailto:foo@bar.example.com">foo@bar.example.com</a></p>

Example 613

Markdown	HTML	Demo
<foo+special@Bar.baz-bar0.com>	<p><a href="mailto:foo+special@Bar.baz-bar0.com">foo+special@Bar.baz-bar0.com</a></p>

Backslash-escapes do not work inside email autolinks:

Example 614

Markdown	HTML	Demo
<foo\+@bar.example.com>	<p>&lt;foo+@bar.example.com&gt;</p>

These are not autolinks:

Example 615

Markdown	HTML	Demo
<>	<p>&lt;&gt;</p>

Example 616

Markdown	HTML	Demo
< http://foo.bar >	<p>&lt; http://foo.bar &gt;</p>

Example 617

Markdown	HTML	Demo
<m:abc>	<p>&lt;m:abc&gt;</p>

Example 618

Markdown	HTML	Demo
<foo.bar.baz>	<p>&lt;foo.bar.baz&gt;</p>

Example 619

Markdown	HTML	Demo
http://example.com	<p>http://example.com</p>

Example 620

Markdown	HTML	Demo
foo@bar.example.com	<p>foo@bar.example.com</p>