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<!DOCTYPE html><html lang="en-US"><meta charset="utf-8">
<title>URL Standard</title>
<link href="http://www.whatwg.org/style/specification" rel="stylesheet">
<link href="//resources.whatwg.org/logo-url.svg" rel="icon">
<div class="head">
<p><a class="logo" href="//www.whatwg.org/"><img alt="WHATWG" height="100" src="//resources.whatwg.org/logo-url.svg" width="100"></a></p>
<h1>URL</h1>
<h2 class="no-num no-toc" id="living-standard-—-last-updated-15-january-2014">Living Standard — Last Updated 15 January 2014</h2>
<dl>
<dt>This Version:
<dd><a href="//url.spec.whatwg.org/">http://url.spec.whatwg.org/</a>
<dt>Participate:</dt>
<dd>Send feedback to
<a href="http://www.whatwg.org/mailing-list">whatwg@whatwg.org</a>
(<a href="http://www.whatwg.org/mailing-list#specs">archives</a>) or
<a href="https://www.w3.org/Bugs/Public/enter_bug.cgi?product=WHATWG&component=URL">file a bug</a>
(<a href="https://www.w3.org/Bugs/Public/buglist.cgi?product=WHATWG&component=URL&resolution=---">open bugs</a>)
<dd><a href="http://wiki.whatwg.org/wiki/IRC">IRC: #whatwg on Freenode</a>
<dt>Version History:
<dd><a href="https://github.com/whatwg/url/commits">https://github.com/whatwg/url/commits</a>
<dd><a href="https://twitter.com/urlstandard">@urlstandard</a>
<dt>Editor:
<dd class="h-card vcard"><a class="u-url url p-name fn" href="http://annevankesteren.nl/" lang="nl">Anne van Kesteren</a>
<<a class="u-email email" href="mailto:annevk@annevk.nl">annevk@annevk.nl</a>>
</dl>
<script async="" src="//resources.whatwg.org/file-bug.js"></script>
<p class="copyright"><a href="http://creativecommons.org/publicdomain/zero/1.0/" rel="license"><img alt="CC0" src="http://i.creativecommons.org/p/zero/1.0/80x15.png"></a>
To the extent possible under law, the editors have waived all copyright and
related or neighboring rights to this work. In addition, as of
15 January 2014, the editors have made this specification available
under the
<a href="http://www.openwebfoundation.org/legal/the-owf-1-0-agreements/owfa-1-0" rel="license">Open Web Foundation Agreement Version 1.0</a>,
which is available at
http://www.openwebfoundation.org/legal/the-owf-1-0-agreements/owfa-1-0.
</div>
<h2 class="no-num no-toc" id="table-of-contents">Table of Contents</h2>
<!--begin-toc-->
<ol class="toc">
<li><a class="no-num" href="#goals">Goals</a></li>
<li><a href="#conformance"><span class="secno">1 </span>Conformance</a></li>
<li><a href="#terminology"><span class="secno">2 </span>Terminology</a>
<ol>
<li><a href="#parsers"><span class="secno">2.1 </span>Parsers</a></ol></li>
<li><a href="#percent-encoded-bytes"><span class="secno">3 </span>Percent-encoded bytes</a></li>
<li><a href="#hosts-(domains-and-ip-addresses)"><span class="secno">4 </span>Hosts (domains and IP addresses)</a>
<ol>
<li><a href="#idna"><span class="secno">4.1 </span>IDNA</a></li>
<li><a href="#host-writing"><span class="secno">4.2 </span>Writing</a></li>
<li><a href="#host-parsing"><span class="secno">4.3 </span>Parsing</a></li>
<li><a href="#host-serializing"><span class="secno">4.4 </span>Serializing</a></ol></li>
<li><a href="#urls"><span class="secno">5 </span>URLs</a>
<ol>
<li><a href="#writing"><span class="secno">5.1 </span>Writing</a></li>
<li><a href="#parsing"><span class="secno">5.2 </span>Parsing</a></li>
<li><a href="#serializing"><span class="secno">5.3 </span>Serializing</a></ol></li>
<li><a href="#application/x-www-form-urlencoded"><span class="secno">6 </span><code>application/x-www-form-urlencoded</code></a>
<ol>
<li><a href="#urlencoded-parsing"><span class="secno">6.1 </span>Parsing</a></li>
<li><a href="#urlencoded-serializing"><span class="secno">6.2 </span>Serializing</a></li>
<li><a href="#urlencoded-hooks"><span class="secno">6.3 </span>Hooks</a></ol></li>
<li><a href="#api"><span class="secno">7 </span>API</a>
<ol>
<li><a href="#constructors"><span class="secno">7.1 </span>Constructors</a></li>
<li><a href="#url-statics"><span class="secno">7.2 </span><code>URL</code> statics</a></li>
<li><a href="#urlutils-and-urlutilsreadonly-members"><span class="secno">7.3 </span><code>URLUtils</code> and <code>URLUtilsReadOnly</code> members</a></li>
<li><a href="#interface-urlsearchparams"><span class="secno">7.4 </span>Interface <code>URLSearchParams</code></a></ol></li>
<li><a class="no-num" href="#references">References</a></li>
<li><a class="no-num" href="#acknowledgments">Acknowledgments</a></ol>
<!--end-toc-->
<h2 class="no-num" id="goals">Goals</h2>
<p>The URL standard sets out to make URLs fully predictable and
interoperable. This is the plan:
<ul>
<li><p>Align RFC 3986 and RFC 3987 with contemporary implementations and
obsolete them in the process. (E.g. spaces, other "illegal" code points,
query encoding, equality, canonicalization, are all concepts not entirely
shared, or defined.) URL parsing needs to become as solid as HTML parsing.
<a class="informative" href="#refsURI">[URI]</a>
<a class="informative" href="#refsIRI">[IRI]</a>
<li><p>Standardize on the term URL. URI and IRI are just confusing. In
practice a single algorithm is used for both so keeping them distinct is
not helping anyone. URL also easily wins the
<a href="http://www.googlefight.com/index.php?word1=url&word2=uri">search result popularity contest</a>.
<li><p>Define URL's existing JavaScript API in full detail and add
enhancements to make it easier to work with. Add a new <a href="#url"><code>URL</code></a>
object as well for URL manipulation without usage of HTML elements. (Useful
for Web Workers.)
</ul>
<p class="note">As the editor learns more about the subject matter the goals
might increase in scope somewhat.
<h2 id="conformance"><span class="secno">1 </span>Conformance</h2>
<p>All diagrams, examples, and notes in this specification are
non-normative, as are all sections explicitly marked non-normative.
Everything else in this specification is normative.
<p>The key words "MUST", "MUST NOT", "REQUIRED", <!--"SHALL", "SHALL
NOT",--> "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in the normative parts of this specification are to be
interpreted as described in RFC2119. For readability, these words do
not appear in all uppercase letters in this specification.
<a href="#refsRFC2119">[RFC2119]</a>
<h2 id="terminology"><span class="secno">2 </span>Terminology</h2>
<p>Some terms used in this specification are defined in the
Encoding Standard. <a href="#refsENCODING">[ENCODING]</a>
<p>The <dfn id="ascii-digits">ASCII digits</dfn> are code points in the range U+0030 to U+0039.
<!-- XXX ref Encoding? -->
<p>The <dfn id="ascii-hex-digits">ASCII hex digits</dfn> are <a href="#ascii-digits">ASCII digits</a> or are
code points in the range U+0041 to U+0046 or in the range U+0061 to U+0066.
<p>The <dfn id="ascii-alpha">ASCII alpha</dfn> are code points in the range U+0041 to U+005A
or in the range U+0061 to U+007A.
<p>The <dfn id="ascii-alphanumeric">ASCII alphanumeric</dfn> are <a href="#ascii-digits">ASCII digits</a> or
<a href="#ascii-alpha">ASCII alpha</a>.
<p>The <dfn id="domain-label-separators">domain label separators</dfn> are the code points
U+002E, U+3002, U+FF0E, and U+FF61.
<!-- IDNA2003/UTS #46; IDNA2008 does not define these -->
<h3 id="parsers"><span class="secno">2.1 </span>Parsers</h3>
<p>The <dfn id="eof-code-point">EOF code point</dfn> is a conceptual code point that signifies the end of a
string or code point stream.
<p>A <dfn id="parse-error">parse error</dfn> indicates a non-fatal mismatch between input and requirements.
User agents are encouraged to expose <a href="#parse-error" title="parse error">parse errors</a>
somehow.
<p>Within a parser algorithm that uses a <var title="">pointer</var> variable, <dfn id="c">c</dfn>
references the code point the <var title="">pointer</var> variable points to.
<p>Within a string-based parser algorithm that uses a <var title="">pointer</var> variable,
<dfn id="remaining">remaining</dfn> references the substring after <var title="">pointer</var> in the string
being processed.
<p class="example">If "<code title="">mailto:example@example</code>" is a string being
processed and <var title="">pointer</var> points to "<code title="">@</code>",
<a href="#c">c</a> is "<code title="">@</code>" and <a href="#remaining">remaining</a> is
"<code title="">example</code>".
<h2 id="percent-encoded-bytes"><span class="secno">3 </span>Percent-encoded bytes</h2>
<p>A <dfn id="percent-encoded-byte">percent-encoded byte</dfn> is "<code title="">%</code>", followed by
two <a href="#ascii-hex-digits">ASCII hex digits</a>. Sequences of
<a href="#percent-encoded-byte" title="percent-encoded byte">percent-encoded bytes</a>, after
conversion to bytes, should not cause
<a class="external" data-anolis-spec="encoding" href="http://encoding.spec.whatwg.org/#utf-8-decode">utf-8 decode</a> to run into any
<a class="external" data-anolis-spec="encoding" href="http://encoding.spec.whatwg.org/#error" title="error">errors</a>.
<p>To <dfn id="percent-encode">percent encode</dfn> a <var title="">byte</var> into a
<a href="#percent-encoded-byte">percent-encoded byte</a>, return a string consisting of
"<code title="">%</code>", followed by a double-digit, uppercase, hexadecimal
representation of <var title="">byte</var>.
<p>To <dfn id="percent-decode">percent decode</dfn> a byte sequence <var title="">input</var>, run these steps:
<p class="warning">Using anything but <a class="external" data-anolis-spec="encoding" href="http://encoding.spec.whatwg.org/#utf-8">utf-8</a>'s
<a class="external" data-anolis-spec="encoding" href="http://encoding.spec.whatwg.org/#decoder">decoder</a> when the <var title="">input</var> contains
bytes outside the range 0x00 to 0x7F might be insecure and is not recommended.
<ol>
<li><p>Let <var title="">output</var> be an empty byte sequence.
<li>
<p>For each byte <var title="">byte</var> in <var title="">input</var>, run these steps:
<ol>
<li><p>If <var title="">byte</var> is not `<code title="">%</code>`, append
<var title="">byte</var> to <var title="">output</var>.
<li><p>Otherwise, if <var title="">byte</var> is `<code title="">%</code>` and the next two
bytes after <var title="">byte</var> in <var title="">input</var> are not in the ranges
0x30 to 0x39, 0x41 to 0x46, and 0x61 to 0x66, append <var title="">byte</var> to
<var title="">output</var>.
<li>
<p>Otherwise, run these substeps:
<ol>
<li><p>Let <var title="">bytePoint</var> be the two bytes after <var title="">byte</var> in
<var title="">input</var>,
<a class="external" data-anolis-spec="encoding" href="http://encoding.spec.whatwg.org/#utf-8-encode" title="utf-8 encode">encoded</a>, and then
interpreted as hexadecimal number.
<!-- We should have a definition for this that is saner. -->
<li><p>Append a byte whose value is <var title="">bytePoint</var> to
<var title="">output</var>.
<li><p>Skip the next two bytes in <var title="">input</var>.
</ol>
</ol>
<li><p>Return <var title="">bytes</var>.
</ol>
<!-- the escape sets are minimal as escaping can lead to problems; we might
be able to escape more here but only if implementors are willing and
there's an upside
note that query and application/x-www-form-urlencoded use their own
local sets -->
<p>The <dfn id="simple-encode-set">simple encode set</dfn> are all code points less than
U+0020 (i.e. excluding U+0020) and all code points greater than U+007E.
<p>The <dfn id="default-encode-set">default encode set</dfn> is the
<a href="#simple-encode-set">simple encode set</a> and code points U+0020,
'<code title="">"</code>', <!-- 0x22 -->
"<code title="">#</code>", <!-- 0x23 -->
"<code title=""><</code>", <!-- 0x3C -->
"<code title="">></code>", <!-- 0x3E -->
"<code title="">?</code>", <!-- 0x3F -->
and
"<code title="">`</code>". <!-- 0x60 -->
<p>The <dfn id="password-encode-set">password encode set</dfn> is the
<a href="#default-encode-set">default encode set</a> and code points
"<code title="">/</code>", <!-- 0x2F -->
"<code title="">@</code>", <!-- 0x40 -->
and
"<code title="">\</code>". <!-- 0x5C -->
<p>The <dfn id="username-encode-set">username encode set</dfn> is the
<a href="#password-encode-set">password encode set</a> and code point
"<code title="">:</code>". <!-- 0x3A -->
<p>To <dfn id="utf-8-percent-encode">utf-8 percent encode</dfn> a <var title="">code point</var>, using
an <var title="">encode set</var>, run these steps:
<ol>
<li><p>If <var title="">code point</var> is not in
<var title="">encode set</var>, return <var title="">code point</var>.
<li><p>Let <var title="">bytes</var> be the result of running
<a class="external" data-anolis-spec="encoding" href="http://encoding.spec.whatwg.org/#utf-8-encode">utf-8 encode</a> on
<var title="">code point</var>.
<li><p><a href="#percent-encode">Percent encode</a> each byte in <var title="">bytes</var>, and
then return them concatenated, in the same order.
</ol>
<h2 id="hosts-(domains-and-ip-addresses)"><span class="secno">4 </span>Hosts (domains and IP addresses)</h2>
<!-- Punycode:
http://tools.ietf.org/html/rfc3492
http://mothereff.in/punycode -->
<p>A <dfn id="concept-host" title="concept-host">host</dfn> is null or a network address in the form of either
a <a href="#concept-domain" title="concept-domain">domain</a> or an
<a href="#concept-ipv6" title="concept-ipv6">IPv6 address</a>.
<p>A <dfn id="concept-domain" title="concept-domain">domain</dfn> is an ordered list of one or
more <dfn id="concept-domain-label" title="concept-domain-label">domain labels</dfn>.
<p>An <dfn id="concept-ipv6" title="concept-ipv6">IPv6 address</dfn> is a 128-bit identifier and
for the purposes of this specification represented as an ordered list of
eight <dfn id="concept-ipv6-piece" title="concept-ipv6-piece">16-bit pieces</dfn>.
<a class="informative" href="#refsIPV6">[IPV6]</a>
<h3 id="idna"><span class="secno">4.1 </span>IDNA</h3>
<p>The <dfn id="concept-domain-label-to-ascii" title="concept-domain-label-to-ascii">domain label to ASCII</dfn> algorithm is
the <a class="external" data-anolis-spec="idna" href="http://tools.ietf.org/html/rfc3490#section-4.1" title="ToASCII">IDNA2003 ToASCII algorithm</a> with the
AllowUnassigned flag set and the version of Unicode used being the most recent version
rather than Unicode 3.2.
<p>The <dfn id="concept-domain-label-to-unicode" title="concept-domain-label-to-unicode">domain label to Unicode</dfn> algorithm
is the <a class="external" data-anolis-spec="idna" href="http://tools.ietf.org/html/rfc3490#section-4.2" title="ToUnicode">IDNA2003 ToUnicode algorithm</a>
with the AllowUnassigned flag set and the version of Unicode used being the most recent
version rather than Unicode 3.2.
<a href="#refsIDNA">[IDNA]</a>
<a href="#refsUNICODE">[UNICODE]</a>
<p class="note">Using the latest version of Unicode as well as IDNA2003 rather than IDNA2008
are willful violations, to be compatible with widely deployed clients.
<p>The <dfn id="concept-domain-to-ascii" title="concept-domain-to-ascii">domain to ASCII</dfn> algorithm takes a
<a href="#concept-domain" title="concept-domain">domain</a> <var title="">input</var> and then runs these steps:
<ol>
<li><p>Let <var title="">asciiLabels</var> be an empty list.
<li><p>On each <a href="#concept-domain-label" title="concept-domain-label">domain label</a> in
<var title="">input</var>, in order, run the
<a href="#concept-domain-label-to-ascii" title="concept-domain-label-to-ascii">domain label to ASCII</a> algorithm.
If that operation failed, return failure.
Otherwise, append the result to <var title="">asciiLabels</var>.
<li><p>Return <var title="">asciiLabels</var>.
</ol>
<p>The <dfn id="concept-domain-to-unicode" title="concept-domain-to-unicode">domain to Unicode</dfn> algorithm takes a
<a href="#concept-domain" title="concept-domain">domain</a> <var title="">input</var> and then runs these steps:
<ol>
<li><p>Let <var title="">unicodeLabels</var> be an empty list.
<li>
<p>On each <a href="#concept-domain-label" title="concept-domain-label">domain label</a> in
<var title="">input</var>, in order, run the
<a href="#concept-domain-label-to-unicode" title="concept-domain-label-to-unicode">domain label to Unicode</a> algorithm and
append the result to <var title="">unicodeLabels</var>.
<p class="note">Note that the
<a href="#concept-domain-label-to-unicode" title="concept-domain-label-to-unicode">domain label to Unicode</a> algorithm
cannot fail.
<li><p>Return <var title="">unicodeLabels</var>.
</ol>
<h3 id="host-writing"><span class="secno">4.2 </span>Writing</h3>
<p>A <a href="#concept-host" title="concept-host">host</a> must be either a
<a href="#concept-domain" title="concept-domain">domain</a> or "<code title="">[</code>", followed
by an <a href="#concept-ipv6" title="concept-ipv6">IPv6 address</a>, followed by
"<code title="">]</code>".
<p>A <a href="#concept-domain" title="concept-domain">domain</a> is one or more
<a href="#concept-domain-label" title="concept-domain-label">domain labels</a> separated from each
other by a
<a href="#domain-label-separators" title="domain label separators">domain label separator</a>,
optionally followed by a
<a href="#domain-label-separators" title="domain label separators">domain label separator</a>.
<p class="note">A trailing
<a href="#domain-label-separators" title="domain label separators">domain label separator</a>
signifies an empty <a href="#concept-domain-label" title="concept-domain-label">domain label</a>.
<!-- if a domain has 4 labels, no trailing dot, and each label consists only
of ASCII digits it's IPv4 because the last label of a domain cannot
start with an ASCII digit -->
<p class="XXX">A <a href="#concept-domain-label" title="concept-domain-label">domain label</a> is ...
<p>An <a href="#concept-ipv6" title="concept-ipv6">IPv6 address</a> is defined in the
<a href="http://tools.ietf.org/html/rfc4291#section-2.2">"Text Representation of Addresses" chapter of IP Version 6 Addressing Architecture</a>.
<a href="#refsIPV6">[IPV6]</a>
<!-- http://tools.ietf.org/html/rfc5952 updates that RFC, but it seems as
far as what developers can do we should be liberal
XXX should we define the format inline instead just like STD 66? -->
<h3 id="host-parsing"><span class="secno">4.3 </span>Parsing</h3>
<p>The <dfn id="concept-host-parser" title="concept-host-parser">host parser</dfn> takes a string
<var title="">input</var> and optionally a <var title="">Unicode flag</var>, and then runs
these steps:
<ol>
<li><p>If <var title="">input</var> is the empty string, return failure.
<!-- Otherwise parsing URLs would not be idempotent:
http://@/example.org/ -> http:///example.org/ -> http://example.org/
Could potentially move this check to the URL parser if deemed problematic. -->
<li>
<p>If <var title="">input</var> starts with "<code title="">[</code>", run these
substeps:
<ol>
<li><p>If <var title="">input</var> does not end with
"<code title="">]</code>", <a href="#parse-error">parse error</a>, return failure.
<li><p>Return the result of
<a href="#concept-ipv6-parser" title="concept-ipv6-parser">IPv6 parsing</a> <var title="">input</var>
with its leading "<code title="">[</code>" and trailing
"<code title="">]</code>" removed.
</ol>
<li><p>Let <var title="">host</var> be the result of running
<a class="external" data-anolis-spec="encoding" href="http://encoding.spec.whatwg.org/#utf-8-decode">utf-8 decode</a> on the
<a href="#percent-decode" title="percent decode">percent decoding</a> of running
<a class="external" data-anolis-spec="encoding" href="http://encoding.spec.whatwg.org/#utf-8-encode">utf-8 encode</a> on <var title="">input</var>.
<!-- https://bugzilla.mozilla.org/show_bug.cgi?id=309671 -->
<li><p>Let <var title="">domain</var> be the result of splitting <var title="">host</var> on
any <a href="#domain-label-separators">domain label separators</a>.
<li><p>Let <var title="">asciiDomain</var> be the result of running
<a href="#concept-domain-to-ascii" title="concept-domain-to-ascii">domain to ASCII</a> on <var title="">domain</var>.
<li><p>If <var title="">asciiDomain</var> is failure, return failure.
<li>
<p>For each <a href="#concept-domain-label" title="concept-domain-label">label</a> <var title="">asciiLabel</var> in
<var title="">asciiDomain</var>, and then for each code point <var title="">cp</var> in
<var title="">asciiLabel</var>, depending on <var title="">cp</var>:
<dl class="switch">
<dt><a href="#ascii-alpha">ASCII alpha</a>
<dd>Lowercase <var title="">cp</var> in <var title="">asciiLabel</var>.
<dt>U+0000
<dt>U+0009
<dt>U+000A
<dt>U+000D
<dt>U+0020
<dt>"<code title="">#</code>"<!-- 23 -->
<dt>"<code title="">%</code>"<!-- 25 -->
<dt>"<code title="">/</code>"<!-- 2F -->
<dt>"<code title="">:</code>"<!-- 3A -->
<dt>"<code title="">?</code>"<!-- 3F -->
<dt>"<code title="">@</code>"<!-- 40 -->
<dt>"<code title="">\</code>"<!-- 5C -->
<dd>Return failure.
<dt>Otherwise
<dd>Do nothing.
</dl>
<li><p>Return <var title="">asciiDomain</var> if the <var title="">Unicode flag</var> is unset,
and the result of running <a href="#concept-domain-to-unicode" title="concept-domain-to-unicode">domain to Unicode</a>
on <var title="">asciiDomain</var> otherwise.
</ol>
<p>The <dfn id="concept-ipv6-parser" title="concept-ipv6-parser">IPv6 parser</dfn> takes a string
<var title="">input</var> and then runs these steps:
<ol>
<li><p>Let <var title="">address</var> be a new
<a href="#concept-ipv6" title="concept-ipv6">IPv6 address</a> with its
<a href="#concept-ipv6-piece" title="concept-ipv6-piece">16-bit pieces</a> initialized to 0.
<li><p>Let <var title="">piece pointer</var> be a pointer into
<var title="">address</var>'s
<a href="#concept-ipv6-piece" title="concept-ipv6-piece">16-bit pieces</a>, initially zero
(pointing to the first <a href="#concept-ipv6-piece" title="concept-ipv6-piece">16-bit piece</a>),
and let <var title="">piece</var> be the
<a href="#concept-ipv6-piece" title="concept-ipv6-piece">16-bit piece</a> it points to.
<li><p>Let <var title="">compress pointer</var> be another pointer into
<var title="">pieces</var>, initially null and pointing to nothing.
<li><p>Let <var title="">pointer</var> be a pointer into
<var title="">input</var>, initially zero (pointing to the first code point).
<li>
<p>If <a href="#c">c</a> is "<code title="">:</code>", run these substeps:
<ol>
<li><p>If <a href="#remaining">remaining</a> does not start with
"<code title="">:</code>", <a href="#parse-error">parse error</a>, return failure.
<li><p>Increase <var title="">pointer</var> by two.
<li><p>Increase <var title="">piece pointer</var> by one and then set
<var title="">compress pointer</var> to <var title="">piece pointer</var>.
</ol>
<li>
<p><dfn id="concept-ipv6-parser-main" title="concept-ipv6-parser-main">Main</dfn>:
While <a href="#c">c</a> is not the <a href="#eof-code-point">EOF code point</a>, run these
substeps:
<ol>
<li><p>If <var title="">piece pointer</var> is eight,
<a href="#parse-error">parse error</a>, return failure.
<li>
<p>If <a href="#c">c</a> is "<code title="">:</code>", run these inner
substeps:
<ol>
<li><p>If <var title="">compress pointer</var> is not null,
<a href="#parse-error">parse error</a>, return failure.
<li>Increase <var title="">pointer</var> and <var title="">piece pointer</var> by one, set
<var title="">compress pointer</var> to <var title="">piece pointer</var>,
and then jump to <a href="#concept-ipv6-parser-main" title="concept-ipv6-parser-main">Main</a>.
</ol>
<li><p>Let <var title="">value</var> and <var title="">length</var> be 0.
<li><p>While <var title="">length</var> is less than 4 and
<a href="#c">c</a> is an
<a href="#ascii-hex-digits" title="ASCII hex digits">ASCII hex digit</a>, set
<var title="">value</var> to
<var title="">value</var> × 0x10 + <a href="#c">c</a> interpreted as hexadecimal number,
and increase <var title="">pointer</var> and <var title="">length</var> by one.
<li>
<p>Based on <a href="#c">c</a>:
<dl class="switch">
<dt>"<code title="">.</code>"
<dd>
<p>If <var title="">length</var> is 0, <a href="#parse-error">parse error</a>,
return failure.
<p>Decrease <var title="">pointer</var> by <var title="">length</var>.
<p>Jump to <a href="#concept-ipv6-parser-ipv4" title="concept-ipv6-parser-ipv4">IPv4</a>.
<dt>"<code title="">:</code>"
<dd>
<p>Increase <var title="">pointer</var> by one.
<p>If <a href="#c">c</a> is the <a href="#eof-code-point">EOF code point</a>,
<a href="#parse-error">parse error</a>, return failure.
<dt>Anything but the <a href="#eof-code-point">EOF code point</a>
<dd><p><a href="#parse-error">Parse error</a>, return failure.
</dl>
<li><p>Set <var title="">piece</var> to <var title="">value</var>.
<li><p>Increase <var title="">piece pointer</var> by one.
</ol>
<li><p>If <a href="#c">c</a> is the <a href="#eof-code-point">EOF code point</a>, jump to
<a href="#concept-ipv6-parser-finale" title="concept-ipv6-parser-finale">Finale</a>.
<li><p><dfn id="concept-ipv6-parser-ipv4" title="concept-ipv6-parser-ipv4">IPv4</dfn>:
If <var title="">piece pointer</var> is greater than six,
<a href="#parse-error">parse error</a>, return failure.
<li><p>Let <var title="">dots seen</var> be 0.
<li>
<p>While <a href="#c">c</a> is not the <a href="#eof-code-point">EOF code point</a>, run
these substeps:
<ol>
<li><p>Let <var title="">value</var> be 0.
<li><p>If <a href="#c">c</a> is not an <a href="#ascii-digits" title="ASCII digits">ASCII digit</a>,
<a href="#parse-error">parse error</a>, return failure. <!-- prevent the empty string -->
<li><p>While <a href="#c">c</a> is an
<a href="#ascii-digits" title="ASCII digits">ASCII digit</a>, set <var title="">value</var> to
<var title="">value</var> × 10 + <a href="#c">c</a> interpreted as decimal number
and increase <var title="">pointer</var> by one.
<li><p>If <var title="">value</var> is greater than 255,
<a href="#parse-error">parse error</a>, return failure.
<li><p>If <var title="">dots seen</var> is less than 3 and
<a href="#c">c</a> is not a "<code title="">.</code>",
<a href="#parse-error">parse error</a>, return failure.
<li><p>Set <var title="">piece</var> to
<var title="">piece</var> × 0x100 + <var title="">value</var>.
<li><p>If <var title="">dots seen</var> is 0 or 2, increase
<var title="">piece pointer</var> by one.
<li><p>Increase <var title="">pointer</var> by one.
<li><p>If <var title="">dots seen</var> is 3 and <a href="#c">c</a> is not
the <a href="#eof-code-point">EOF code point</a>,
<a href="#parse-error">parse error</a>, return failure.
<li><p>Increase <var title="">dots seen</var> by one.
</ol>
<li>
<p><dfn id="concept-ipv6-parser-finale" title="concept-ipv6-parser-finale">Finale</dfn>:
If <var title="">compress pointer</var> is not null, run these substeps:
<ol>
<li><p>Let <var title="">swaps</var> be
<var title="">piece pointer</var> − <var title="">compress pointer</var>.
<li><p>Set <var title="">piece pointer</var> to seven.
<li><p>While <var title="">piece pointer</var> is not zero, swap <var title="">piece</var>
with the <a href="#concept-ipv6-piece" title="concept-ipv6-piece">piece</a> at pointer
<var title="">compress pointer</var> + <var title="">swaps</var> − 1, and then
decrease <var title="">piece pointer</var> and <var title="">swaps</var> by one.
</ol>
<li><p>Otherwise, if <var title="">compress pointer</var> is null and
<var title="">piece pointer</var> is not eight, <a href="#parse-error">parse error</a>,
return failure.
<li><p>Return <var title="">address</var>.
</ol>
<h3 id="host-serializing"><span class="secno">4.4 </span>Serializing</h3>
<p>The <dfn id="concept-host-serializer" title="concept-host-serializer">host serializer</dfn> takes a
<a href="#concept-host" title="concept-host">host</a> <var title="">host</var> and then runs
these steps:
<ol>
<li><p>If <var title="">host</var> is null, return the empty string.
<!-- XXX Are we okay with this? -->
<li><p>If <var title="">host</var> is an
<a href="#concept-ipv6" title="concept-ipv6">IPv6 address</a>, return
"<code title="">[</code>", followed by the result of running the
<a href="#concept-ipv6-serializer" title="concept-ipv6-serializer">IPv6 serializer</a> on <var title="">host</var>,
followed by "<code title="">]</code>".
<li><p>Otherwise, <var title="">host</var> is a <a href="#concept-domain" title="concept-domain">domain</a>,
return its <a href="#concept-domain-label" title="concept-domain-label">labels</a> separated from each other by
U+002E.
</ol>
<p>The <dfn id="concept-ipv6-serializer" title="concept-ipv6-serializer">IPv6 serializer</dfn> takes an
<a href="#concept-ipv6" title="concept-ipv6">IPv6 address</a> <var title="">address</var> and
then runs these steps:
<ol>
<li><p>Let <var title="">output</var> be the empty string.
<li>
<p>Let <var title="">compress pointer</var> be a pointer to the first
<a href="#concept-ipv6-piece" title="concept-ipv6-piece">16-bit piece</a> in the first longest
sequences of <var title="">address</var>'s
<a href="#concept-ipv6-piece" title="concept-ipv6-piece">16-bit pieces</a> that are 0.
<p class="example">In <code title="">0:f:0:0:f:f:0:0</code> it would point to
the second 0.
<li><p>If there is no sequence of <var title="">address</var>'s
<a href="#concept-ipv6-piece" title="concept-ipv6-piece">16-bit pieces</a> that are 0 longer than
one, set <var title="">compress pointer</var> to null.
<li>
<p>For each <var title="">piece</var> in <var title="">address</var>'s
<a href="#concept-ipv6-piece" title="concept-ipv6-piece">pieces</a>, run these substeps:
<ol>
<li><p>If <var title="">compress pointer</var> points to
<var title="">piece</var>, append "<code title="">::</code>" to
<var title="">output</var> if <var title="">piece</var> is
<var title="">address</var>'s first <a href="#concept-ipv6-piece" title="concept-ipv6-piece">piece</a> and append
"<code title="">:</code>" otherwise, and then run these substeps again with all
subsequent <a href="#concept-ipv6-piece" title="concept-ipv6-piece">pieces</a> in
<var title="">address</var>'s <a href="#concept-ipv6-piece" title="concept-ipv6-piece">pieces</a>
that are 0 skipped or go the next step in the overall set of steps if
that leaves no <a href="#concept-ipv6-piece" title="concept-ipv6-piece">pieces</a>.
<li><p>Append <var title="">piece</var>, represented as the shortest
possible lowercase hexadecimal number, to <var title="">output</var>.
<li><p>If <var title="">piece</var> is not
<var title="">address</var>'s last <a href="#concept-ipv6-piece" title="concept-ipv6-piece">piece</a>,
append "<code title="">:</code>" to <var title="">output</var>.
</ol>
<li><p>Return <var title="">output</var>.
</ol>
<p class="note">This algorithm requires the recommendation from
A Recommendation for IPv6 Address Text Representation.
<a class="informative" href="#refsIPV6TEXT">[IPV6TEXT]</a>
<!-- Safari/Gecko/Opera do not normalize IPv6. Chrome does. This algorithm
follows Chrome because we normalize domains too. -->
<h2 id="urls"><span class="secno">5 </span>URLs</h2>
<!-- History behind URL as term:
http://lists.w3.org/Archives/Public/uri/2012Oct/0080.html -->
<p>A <dfn id="concept-url" title="concept-url">URL</dfn> is a string that represents an
identifier.
<p>A <a href="#concept-url" title="concept-url">URL</a> is either a
<a href="#concept-relative-url" title="concept-relative-url">relative URL</a> or an
<a href="#concept-absolute-url" title="concept-absolute-url">absolute URL</a>. Either form can be
followed by a <a href="#concept-url-fragment" title="concept-url-fragment">fragment</a>.
<p>A <dfn id="concept-relative-url" title="concept-relative-url">relative URL</dfn> is a
<a href="#concept-url" title="concept-url">URL</a> without a <a href="#concept-url-scheme" title="concept-url-scheme">scheme</a>.
A <a href="#concept-relative-url" title="concept-relative-url">relative URL</a> must be relative
to a <a href="#concept-base-url" title="concept-base-url">base URL</a>.
<p>An <dfn id="concept-absolute-url" title="concept-absolute-url">absolute URL</dfn> is a
<a href="#concept-url" title="concept-url">URL</a> with a <a href="#concept-url-scheme" title="concept-url-scheme">scheme</a>.
<p>A <dfn id="concept-base-url" title="concept-base-url">base URL</dfn> is an
<a href="#concept-absolute-url" title="concept-absolute-url">absolute URL</a> with a <a href="#relative-scheme">relative scheme</a>.
<p><a href="#concept-url-parser" title="concept-url-parser">Parsing</a> (provided it does not
return failure) and <a href="#concept-url-serializer" title="concept-url-serializer">serializing</a> a
<a href="#concept-url" title="concept-url">URL</a> will turn it into an
<a href="#concept-absolute-url" title="concept-absolute-url">absolute URL</a>. The intermediate form
is named a <dfn id="concept-parsed-url" title="concept-parsed-url">parsed URL</dfn>. The components a
<a href="#concept-url" title="concept-url">URL</a> can consist of, and a
<a href="#concept-parsed-url" title="concept-parsed-url">parsed URL</a> consists of, are
<dfn id="concept-url-scheme" title="concept-url-scheme">scheme</dfn>,
<dfn id="concept-url-scheme-data" title="concept-url-scheme-data">scheme data</dfn> (not used if
<a href="#concept-url-scheme" title="concept-url-scheme">scheme</a> is a <a href="#relative-scheme">relative scheme</a>),
<dfn id="concept-url-username" title="concept-url-username">username</dfn>,
<dfn id="concept-url-password" title="concept-url-password">password</dfn>,
<dfn id="concept-url-host" title="concept-url-host">host</dfn>,
<dfn id="concept-url-port" title="concept-url-port">port</dfn>,
<dfn id="concept-url-path" title="concept-url-path">path</dfn>,
<dfn id="concept-url-query" title="concept-url-query">query</dfn>, and
<dfn id="concept-url-fragment" title="concept-url-fragment">fragment</dfn>.
<p>A <dfn id="relative-scheme">relative scheme</dfn> is a
<a href="#concept-url-scheme" title="concept-url-scheme">scheme</a> listed in the first column of
the following table. A <dfn id="default-port">default port</dfn> is a
<a href="#relative-scheme">relative scheme</a>'s optional corresponding
<a href="#concept-url-port" title="concept-url-port">port</a> and is listed in the second column
on the same row.
<table>
<tr><th><a href="#concept-url-scheme" title="concept-url-scheme">scheme</a>
<th><a href="#concept-url-port" title="concept-url-port">port</a>
<tr><td>"<code title="">ftp</code>"<td>"<code title="">21</code>"
<tr><td>"<code title="">file</code>"<td>
<tr><td>"<code title="">gopher</code>"<td>"<code title="">70</code>"
<tr><td>"<code title="">http</code>"<td>"<code title="">80</code>"
<tr><td>"<code title="">https</code>"<td>"<code title="">443</code>"
<tr><td>"<code title="">ws</code>"<td>"<code title="">80</code>"
<tr><td>"<code title="">wss</code>"<td>"<code title="">443</code>"
</table>
<!-- The best reason I have for listing "gopher" is Google does it too:
https://code.google.com/p/google-url/source/browse/trunk/src/url_canon_stdurl.cc#120
It seems fine to remain compatible on that front, no need to support it
elsewhere though. -->
<h3 id="writing"><span class="secno">5.1 </span>Writing</h3>
<!-- http://tantek.com/2011/238/b1/many-ways-slice-url-name-pieces -->
<p>A <a href="#concept-url" title="concept-url">URL</a> must be either a
<a href="#concept-relative-url" title="concept-relative-url">relative URL</a> or an
<a href="#concept-absolute-url" title="concept-absolute-url">absolute URL</a>, optionally followed by
"<code title="">#</code>" and a
<a href="#concept-url-fragment" title="concept-url-fragment">fragment</a>.
<p>An <a href="#concept-absolute-url" title="concept-absolute-url">absolute URL</a> must be a
<a href="#concept-url-scheme" title="concept-url-scheme">scheme</a>, followed by
"<code title="">:</code>", followed by
<a href="#concept-url-scheme-data" title="concept-url-scheme-data">scheme data</a>, optionally followed
by "<code title="">?</code>" and a <a href="#concept-url-query" title="concept-url-query">query</a>.
<p>A <a href="#concept-url-scheme" title="concept-url-scheme">scheme</a> must be one
<a href="#ascii-alpha">ASCII alpha</a>, followed by zero or more of
<a href="#ascii-alphanumeric">ASCII alphanumeric</a>, "<code title="">+</code>",
"<code title="">-</code>", and "<code title="">.</code>". A
<a href="#concept-url-scheme" title="concept-url-scheme">scheme</a> must be registered
<span class="XXX">...</span>.
<p>The syntax of <a href="#concept-url-scheme-data" title="concept-url-scheme-data">scheme data</a>
depends on the <a href="#concept-url-scheme" title="concept-url-scheme">scheme</a> and is typically
defined alongside it. For a <a href="#relative-scheme">relative scheme</a>,
<a href="#concept-url-scheme-data" title="concept-url-scheme-data">scheme data</a> must be a
<a href="#concept-scheme-relative-url" title="concept-scheme-relative-url">scheme-relative URL</a>. For
other <a href="#concept-url-scheme" title="concept-url-scheme">schemes</a>, specifications or
standards must define <a href="#concept-url-scheme-data" title="concept-url-scheme-data">scheme data</a>
within the constraints of zero or more <a href="#url-units">URL units</a>.
<p>A <a href="#concept-relative-url" title="concept-relative-url">relative URL</a> must be either a
<a href="#concept-scheme-relative-url" title="concept-scheme-relative-url">scheme-relative URL</a>, an
<a href="#concept-absolute-path-relative-url" title="concept-absolute-path-relative-url">absolute-path-relative URL</a>,
or a <a href="#concept-path-relative-url" title="concept-path-relative-url">path-relative URL</a> that
does not start with a <a href="#concept-url-scheme" title="concept-url-scheme">scheme</a> and
"<code title="">:</code>", optionally followed by a "<code title="">?</code>" and
a <a href="#concept-url-query" title="concept-url-query">query</a>.
<p>A <dfn id="concept-scheme-relative-url" title="concept-scheme-relative-url">scheme-relative URL</dfn> must be
"<code title="">//</code>", optionally followed by
<a href="#concept-url-userinfo" title="concept-url-userinfo">userinfo</a> and "<code title="">@</code>",
followed by a <a href="#concept-host" title="concept-host">host</a>, optionally followed
by "<code title="">:</code>" and a <a href="#concept-url-port" title="concept-url-port">port</a>,
optionally followed by an
<a href="#concept-absolute-path-relative-url" title="concept-absolute-path-relative-url">absolute-path-relative URL</a>.
<p><dfn id="concept-url-userinfo" title="concept-url-userinfo">Userinfo</dfn> must be a
<a href="#concept-url-username" title="concept-url-username">username</a>, optionally followed by a
"<code title="">:</code>" and a
<a href="#concept-url-password" title="concept-url-password">password</a>.
<p>A <a href="#concept-url-username" title="concept-url-username">username</a> must be zero or more
<a href="#url-units">URL units</a>, excluding "<code title="">/</code>",
"<code title="">:</code>, "<code title="">?</code>", and "<code title="">@</code>".
<!-- password without ":" (sorted on ASCII position) -->
<p>A <a href="#concept-url-password" title="concept-url-password">password</a> must be zero or more
<a href="#url-units">URL units</a>, excluding "<code title="">/</code>",
"<code title="">?</code>", and "<code title="">@</code>".
<p>A <a href="#concept-url-port" title="concept-url-port">port</a> must be zero or more
<a href="#ascii-digits">ASCII digits</a>.
<p>An
<dfn id="concept-absolute-path-relative-url" title="concept-absolute-path-relative-url">absolute-path-relative URL</dfn>
must be "<code title="">/</code>", followed by a
<a href="#concept-path-relative-url" title="concept-path-relative-url">path-relative URL</a> that does not
start with "<code title="">/</code>".
<p>A <dfn id="concept-path-relative-url" title="concept-path-relative-url">path-relative URL</dfn> must be zero or
more <a href="#path-segment" title="path segment">path segments</a> separated from each
other by a "<code title="">/</code>".
<p>A <dfn id="path-segment">path segment</dfn> must be zero or more <a href="#url-units">URL units</a>,
excluding "<code title="">/</code>" and "<code title="">?</code>".
<p>A <a href="#concept-url-query" title="concept-url-query">query</a> must be zero or more
<a href="#url-units">URL units</a>.
<p>A <a href="#concept-url-fragment" title="concept-url-fragment">fragment</a> must be zero or more
<a href="#url-units">URL units</a>.
<p>The <dfn id="url-code-points">URL code points</dfn> are <a href="#ascii-alphanumeric">ASCII alphanumeric</a>,
"<code title="">!</code>",<!-- 0x21, sub-delims -->
"<code title="">$</code>",<!-- 0x24, sub-delims -->
"<code title="">&</code>",<!-- 0x26, sub-delims -->
"<code title="">'</code>",<!-- 0x27, sub-delims -->
"<code title="">(</code>",<!-- 0x28, sub-delims -->
"<code title="">)</code>",<!-- 0x29, sub-delims -->
"<code title="">*</code>",<!-- 0x2A, sub-delims -->
"<code title="">+</code>",<!-- 0x2B, sub-delims -->
"<code title="">,</code>",<!-- 0x2C, sub-delims -->
"<code title="">-</code>",<!-- 0x2D, iunreserved -->
"<code title="">.</code>",<!-- 0x2E, iunreserved -->
"<code title="">/</code>",<!-- 0x2F, iquery/ifragment -->
"<code title="">:</code>",<!-- 0x3A, ipchar -->
"<code title="">;</code>",<!-- 0x3B, sub-delims -->
"<code title="">=</code>",<!-- 0x3D, sub-delims -->
"<code title="">?</code>",<!-- 0x3F, iquery/ifragment -->
"<code title="">@</code>",<!-- 0x40, ipchar -->
"<code title="">_</code>",<!-- 0x5F, iunreserved -->
"<code title="">~</code>",<!-- 0x7E, iunreserved -->
and code points in the ranges
U+00A0 to U+D7FF,
U+E000 to <!--U+F8FF,
U+F900 to -->U+FDCF,
U+FDF0 to U+FFFD,<!-- changed relative to IRI from U+FFEF to U+FFFD to align with HTML-->
U+10000 to U+1FFFD,
U+20000 to U+2FFFD,
U+30000 to U+3FFFD,
U+40000 to U+4FFFD,
U+50000 to U+5FFFD,
U+60000 to U+6FFFD,
U+70000 to U+7FFFD,
U+80000 to U+8FFFD,
U+90000 to U+9FFFD,
U+A0000 to U+AFFFD,
U+B0000 to U+BFFFD,
U+C0000 to U+CFFFD,
U+D0000 to U+DFFFD,
U+E1000 to U+EFFFD,
U+F0000 to U+FFFFD,
U+100000 to U+10FFFD.
<!-- XXX https://www.w3.org/Bugs/Public/show_bug.cgi?id=19743 -->
<p class="note">Code points higher than U+009F will be converted to
<a href="#percent-encoded-byte" title="percent-encoded byte">percent-encoded bytes</a> by the
<a href="#concept-url-parser" title="concept-url-parser">URL parser</a>.
<p>The <dfn id="url-units">URL units</dfn> are <a href="#url-code-points">URL code points</a> and
<a href="#percent-encoded-byte" title="percent-encoded byte">percent-encoded bytes</a>.
<h3 id="parsing"><span class="secno">5.2 </span>Parsing</h3>
<p>Aside from the components mentioned earlier, a
<a href="#concept-parsed-url" title="concept-parsed-url">parsed URL</a> also has an associated
<dfn id="relative-flag">relative flag</dfn>.
<p class="note">The <a href="#relative-flag">relative flag</a> exists as checking if a
<a href="#concept-parsed-url" title="concept-parsed-url">parsed URL</a>'s
<a href="#concept-url-scheme" title="concept-url-scheme">scheme</a> is a <a href="#relative-scheme">relative scheme</a> can give
incorrect results due to the <a href="#dom-url-protocol"><code title="dom-URL-protocol">protocol</code></a> attribute.
<!-- XXX maybe disallow setting protocol to non-sensical values -->
<p class="XXX">Add the ability to halt on the first conformance error.
<p>The <dfn id="concept-url-parser" title="concept-url-parser">URL parser</dfn> takes a string
<var title="">input</var>, optionally with a
<a href="#concept-base-url" title="concept-base-url">base URL</a> <var title="">base</var>,
optionally with an <a class="external" data-anolis-spec="encoding" href="http://encoding.spec.whatwg.org/#encoding">encoding</a>
<var title="">encoding override</var>, optionally with an
<a href="#concept-parsed-url" title="concept-parsed-url">parsed URL</a> <var title="">url</var> and a state override
<var title="">state override</var>, and then runs these steps:
<div class="note no-backref">
<p>The <var title="">encoding override</var> argument is a legacy concept only relevant for
HTML. The <var title="">url</var> and <var title="">state override</var> arguments are only for
use by methods of objects implementing the <a href="#urlutils"><code>URLUtils</code></a> interface.
<a class="informative" href="#refsHTML">[HTML]</a>
<p>When the <var title="">url</var> and <var title="">state override</var> arguments are not
passed the <a href="#concept-url-parser" title="concept-url-parser">URL parser</a> returns either a
<a href="#concept-parsed-url" title="concept-parsed-url">parsed URL</a> or failure. If they are passed the
algorithm simply modifies the passed <var title="">url</var> and can terminate without
returning anything.
</div>
<ol>
<li>
<p>If <var title="">url</var> is not given:
<ol>
<li><p>Set <var title="">url</var> to a new
<a href="#concept-parsed-url" title="concept-parsed-url">parsed URL</a>.
<li><p>Set <var title="">url</var>'s <a href="#concept-url-scheme" title="concept-url-scheme">scheme</a>,
<a href="#concept-url-scheme-data" title="concept-url-scheme-data">scheme data</a>,
<a href="#concept-url-username" title="concept-url-username">username</a>, and
<a href="#concept-url-port" title="concept-url-port">port</a> to the empty string,
<a href="#concept-url-password" title="concept-url-password">password</a>,
<a href="#concept-url-host" title="concept-url-host">host</a>,
<a href="#concept-url-query" title="concept-url-query">query</a>, and
<a href="#concept-url-fragment" title="concept-url-fragment">fragment</a> to null,
<a href="#concept-url-path" title="concept-url-path">path</a> to the empty list, and unset its
<a href="#relative-flag">relative flag</a>.
<li><p>Remove any leading and trailing
<a class="external" data-anolis-spec="encoding" href="http://encoding.spec.whatwg.org/#ascii-whitespace">ASCII whitespace</a> from
<var title="">input</var>.
</ol>
<li><p>Let <var title="">state</var> be <var title="">state override</var>
if given, or <a href="#scheme-start-state">scheme start state</a> otherwise.
<li><p>If <var title="">base</var> is not given, set it to null.
<li><p>If <var title="">encoding override</var> is not given, set it to
<a class="external" data-anolis-spec="encoding" href="http://encoding.spec.whatwg.org/#utf-8">utf-8</a>.
<li><p>Let <var title="">buffer</var> be the empty string.
<li><p>Let the <var title="">@ flag</var> and the <var title="">[] flag</var> be
unset.
<li><p>Let <var title="">pointer</var> be a pointer to first code point in
<var title="">input</var>.
<li>
<p>Keep running the following state machine by switching on
<var title="">state</var>, increasing <var title="">pointer</var> by one after
each time it is run, and if after a run <var title="">pointer</var> points to the
<a href="#eof-code-point">EOF code point</a>, go to the next step.
<dl class="switch">
<dt><dfn id="scheme-start-state">scheme start state</dfn>
<dd>
<ol>
<li><p>If <a href="#c">c</a> is an <a href="#ascii-alpha">ASCII alpha</a>,
append <a href="#c">c</a>, lowercased, to <var title="">buffer</var>, and
set <var title="">state</var> to <a href="#scheme-state">scheme state</a>.
<li><p>Otherwise, if <var title="">state override</var> is not given, set
<var title="">state</var> to <a href="#no-scheme-state">no scheme state</a>, and decrease
<var title="">pointer</var> by one.
<li><p>Otherwise, <a href="#parse-error">parse error</a>, terminate this algorithm.
</ol>
<dt><dfn id="scheme-state">scheme state</dfn>
<dd>
<ol>
<li><p>If <a href="#c">c</a> is an <a href="#ascii-alphanumeric">ASCII alphanumeric</a>,
"<code title="">+</code>", "<code title="">-</code>", or
"<code title="">.</code>", append <a href="#c">c</a>, lowercased, to
<var title="">buffer</var>.
<li>
<p>Otherwise, if <a href="#c">c</a> is "<code title="">:</code>", set
<var title="">url</var>'s <a href="#concept-url-scheme" title="concept-url-scheme">scheme</a> to
<var title="">buffer</var>, <var title="">buffer</var> to the empty string,