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<!doctype html><html lang="en">
<head>
<meta charset="utf-8">
<meta content="width=device-width, initial-scale=1, shrink-to-fit=no" name="viewport">
<meta content="#3c790a" name="theme-color">
<title>URL Standard</title>
<link href="https://resources.whatwg.org/standard.css" rel="stylesheet">
<link href="https://resources.whatwg.org/bikeshed.css" rel="stylesheet">
<link href="https://resources.whatwg.org/logo-url.svg" rel="icon">
<meta content="Bikeshed 1.0.0" name="generator">
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<body class="h-entry status-LS">
<div class="head">
<p data-fill-with="logo"><a class="logo" href="https://whatwg.org/"> <img alt="WHATWG" height="100" src="https://resources.whatwg.org/logo-url.svg"> </a> </p>
<hgroup>
<h1 class="p-name no-ref allcaps" id="title">URL</h1>
<h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Living Standard — Last Updated <time class="dt-updated" datetime="2016-08-25">25 August 2016</time></span></h2>
</hgroup>
<div data-fill-with="spec-metadata">
<dl>
<dt>Participate:
<dd><span><a href="https://github.com/whatwg/url">GitHub whatwg/url</a> (<a href="https://github.com/whatwg/url/issues/new">new issue</a>, <a href="https://github.com/whatwg/url/issues">open issues</a>, <a href="https://www.w3.org/Bugs/Public/buglist.cgi?product=WHATWG&component=URL&resolution=---">legacy open bugs</a>)</span>
<dd><span><a href="https://wiki.whatwg.org/wiki/IRC">IRC: #whatwg on Freenode</a></span>
<dt>Commits:
<dd><span><a href="https://github.com/whatwg/url/commits">https://github.com/whatwg/url/commits</a></span>
<dd><span><a href="https://twitter.com/urlstandard">@urlstandard</a></span>
<dt>Translation (non-normative):
<dd><span><span title="Japanese"><a href="https://triple-underscore.github.io/URL-ja.html" hreflang="ja" lang="ja" rel="alternate">日本語</a></span></span>
</dl>
</div>
<div data-fill-with="warning"></div>
</div>
<h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
<div class="p-summary" data-fill-with="abstract">
<p>The URL Standard defines URLs, domains, IP addresses, the <code title="">application/x-www-form-urlencoded</code> format, and their API.</p>
</div>
<nav data-fill-with="table-of-contents" id="toc">
<h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
<ol class="toc" role="directory">
<li><a href="#goals"><span class="secno"></span> <span class="content">Goals</span></a>
<li>
<a href="#infrastructure"><span class="secno">1</span> <span class="content">Infrastructure</span></a>
<ol class="toc">
<li><a href="#parsers"><span class="secno">1.1</span> <span class="content">Parsers</span></a>
<li><a href="#percent-encoded-bytes"><span class="secno">1.2</span> <span class="content">Percent-encoded bytes</span></a>
</ol>
<li><a href="#security-considerations"><span class="secno">2</span> <span class="content">Security considerations</span></a>
<li>
<a href="#hosts-(domains-and-ip-addresses)"><span class="secno">3</span> <span class="content">Hosts (domains and IP addresses)</span></a>
<ol class="toc">
<li><a href="#idna"><span class="secno">3.1</span> <span class="content">IDNA</span></a>
<li><a href="#host-syntax"><span class="secno">3.2</span> <span class="content">Host syntax</span></a>
<li><a href="#host-parsing"><span class="secno">3.3</span> <span class="content">Host parsing</span></a>
<li><a href="#host-serializing"><span class="secno">3.4</span> <span class="content">Host serializing</span></a>
<li><a href="#host-equivalence"><span class="secno">3.5</span> <span class="content">Host equivalence</span></a>
</ol>
<li>
<a href="#urls"><span class="secno">4</span> <span class="content">URLs</span></a>
<ol class="toc">
<li><a href="#url-syntax"><span class="secno">4.1</span> <span class="content">URL syntax</span></a>
<li><a href="#url-parsing"><span class="secno">4.2</span> <span class="content">URL parsing</span></a>
<li><a href="#url-serializing"><span class="secno">4.3</span> <span class="content">URL serializing</span></a>
<li><a href="#url-equivalence"><span class="secno">4.4</span> <span class="content">URL equivalence</span></a>
<li><a href="#origin"><span class="secno">4.5</span> <span class="content">Origin</span></a>
<li><a href="#url-rendering"><span class="secno">4.6</span> <span class="content">URL rendering</span></a>
</ol>
<li>
<a href="#application/x-www-form-urlencoded"><span class="secno">5</span> <span class="content"><code>application/x-www-form-urlencoded</code></span></a>
<ol class="toc">
<li><a href="#urlencoded-parsing"><span class="secno">5.1</span> <span class="content"><code>application/x-www-form-urlencoded</code> parsing</span></a>
<li><a href="#urlencoded-serializing"><span class="secno">5.2</span> <span class="content"><code>application/x-www-form-urlencoded</code> serializing</span></a>
<li><a href="#urlencoded-hooks"><span class="secno">5.3</span> <span class="content">Hooks</span></a>
</ol>
<li>
<a href="#api"><span class="secno">6</span> <span class="content">API</span></a>
<ol class="toc">
<li><a href="#constructors"><span class="secno">6.1</span> <span class="content">Constructors</span></a>
<li><a href="#url-statics"><span class="secno">6.2</span> <span class="content"><code class="idl"><span>URL</span></code> statics</span></a>
<li><a href="#urlutils-members"><span class="secno">6.3</span> <span class="content"><code class="idl"><span>URL</span></code> members</span></a>
<li><a href="#interface-urlsearchparams"><span class="secno">6.4</span> <span class="content">Interface <code class="idl"><span>URLSearchParams</span></code></span></a>
<li><a href="#url-apis-elsewhere"><span class="secno">6.5</span> <span class="content">URL APIs elsewhere</span></a>
</ol>
<li><a href="#acknowledgments"><span class="secno"></span> <span class="content">Acknowledgments</span></a>
<li><a href="#conformance"><span class="secno"></span> <span class="content">Conformance</span></a>
<li>
<a href="#index"><span class="secno"></span> <span class="content">Index</span></a>
<ol class="toc">
<li><a href="#index-defined-here"><span class="secno"></span> <span class="content">Terms defined by this specification</span></a>
<li><a href="#index-defined-elsewhere"><span class="secno"></span> <span class="content">Terms defined by reference</span></a>
</ol>
<li>
<a href="#references"><span class="secno"></span> <span class="content">References</span></a>
<ol class="toc">
<li><a href="#normative"><span class="secno"></span> <span class="content">Normative References</span></a>
<li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
</ol>
<li><a href="#idl-index"><span class="secno"></span> <span class="content">IDL Index</span></a>
</ol>
</nav>
<main>
<script async="" src="https://resources.whatwg.org/file-issue.js"></script>
<script defer="" id="head" src="https://resources.whatwg.org/dfn.js"></script>
<h2 class="no-num heading settled" id="goals"><span class="content">Goals</span></h2>
<p>The URL standard takes the following approach towards making URLs fully interoperable: </p>
<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 data-link-type="biblio" href="#biblio-rfc3986">[RFC3986]</a> <a data-link-type="biblio" href="#biblio-rfc3987">[RFC3987]</a> </p>
<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>. </p>
<li>
<p>Supplanting <a href="https://tools.ietf.org/html/rfc6454#section-4">Origin of a URI [sic]</a>. <a data-link-type="biblio" href="#biblio-rfc6454">[RFC6454]</a> </p>
<li>
<p>Define URL’s existing JavaScript API in full detail and add
enhancements to make it easier to work with. Add a new <code><a class="idl-code" data-link-type="interface" href="#url">URL</a></code> object as well for URL manipulation without usage of HTML elements. (Useful
for JavaScript worker environments.) </p>
</ul>
<p class="note" role="note">As the editors learn more about the subject matter the goals
might increase in scope somewhat. </p>
<h2 class="heading settled" data-level="1" id="infrastructure"><span class="secno">1. </span><span class="content">Infrastructure</span><a class="self-link" href="#infrastructure"></a></h2>
<p>Some terms used in this specification are defined in the
DOM, Encoding, IDNA, and Web IDL Standards. <a data-link-type="biblio" href="#biblio-dom">[DOM]</a> <a data-link-type="biblio" href="#biblio-encoding">[ENCODING]</a> <a data-link-type="biblio" href="#biblio-idna">[IDNA]</a> <a data-link-type="biblio" href="#biblio-webidl">[WEBIDL]</a> </p>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="c0-controls">C0 controls<a class="self-link" href="#c0-controls"></a></dfn> are code points in the range U+0000 to U+001F, inclusive. </p>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="c0-controls-and-space">C0 controls and space<a class="self-link" href="#c0-controls-and-space"></a></dfn> are <a data-link-type="dfn" href="#c0-controls">C0 controls</a> and code point U+0020. </p>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="tab-and-newline">tab and newline<a class="self-link" href="#tab-and-newline"></a></dfn> are code points U+0009, U+000A, and U+000D. </p>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="ascii-digits">ASCII digits<a class="self-link" href="#ascii-digits"></a></dfn> are code points in the range U+0030 to U+0039, inclusive. </p>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="ascii-hex-digits">ASCII hex digits<a class="self-link" href="#ascii-hex-digits"></a></dfn> are <a data-link-type="dfn" href="#ascii-digits">ASCII digits</a>, code points in the range
U+0041 to U+0046, inclusive, and code points in the range U+0061 to U+0066, inclusive. </p>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="ascii-alpha">ASCII alpha<a class="self-link" href="#ascii-alpha"></a></dfn> are code points in the range U+0041 to U+005A, inclusive,
and in the range U+0061 to U+007A, inclusive. </p>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="ascii-alphanumeric">ASCII alphanumeric<a class="self-link" href="#ascii-alphanumeric"></a></dfn> are <a data-link-type="dfn" href="#ascii-digits">ASCII digits</a> and <a data-link-type="dfn" href="#ascii-alpha">ASCII alpha</a>. </p>
<p>An <dfn data-dfn-type="dfn" data-noexport="" id="ascii-string">ASCII string<a class="self-link" href="#ascii-string"></a></dfn> is a <a data-link-type="dfn" href="https://encoding.spec.whatwg.org/#string">string</a> in the range U+0000 to U+007F, inclusive. </p>
<p>To <dfn data-dfn-type="dfn" data-noexport="" id="ascii-lowercase">ASCII lowercase<a class="self-link" href="#ascii-lowercase"></a></dfn> a <a data-link-type="dfn" href="https://encoding.spec.whatwg.org/#string">string</a>, replace all code points in the range
U+0041 to U+005A, inclusive, with the corresponding code points in the range
U+0061 to U+007A, inclusive. </p>
<hr>
<p>To <dfn data-dfn-type="dfn" data-noexport="" id="serialize-an-integer">serialize an integer<a class="self-link" href="#serialize-an-integer"></a></dfn>, represent it as the shortest possible decimal
number. </p>
<hr>
<p>A <dfn data-dfn-type="dfn" data-noexport="" id="windows-drive-letter">Windows drive letter<a class="self-link" href="#windows-drive-letter"></a></dfn> is two code points, of which the first is
an <a data-link-type="dfn" href="#ascii-alpha">ASCII alpha</a> and the second is either "<code>:</code>" or "<code>|</code>". </p>
<p>A <dfn data-dfn-type="dfn" data-noexport="" id="normalized-windows-drive-letter">normalized Windows drive letter<a class="self-link" href="#normalized-windows-drive-letter"></a></dfn> is a <a data-link-type="dfn" href="#windows-drive-letter">Windows drive letter</a> of which
the second code point is "<code>:</code>". </p>
<h3 class="heading settled" data-level="1.1" id="parsers"><span class="secno">1.1. </span><span class="content">Parsers</span><a class="self-link" href="#parsers"></a></h3>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="eof-code-point">EOF code point<a class="self-link" href="#eof-code-point"></a></dfn> is a conceptual code point that signifies the end of a
string or code point stream. </p>
<p>Within a parser algorithm that uses a <var>pointer</var> variable, <dfn data-dfn-type="dfn" data-noexport="" id="c">c<a class="self-link" href="#c"></a></dfn> references the code point the <var>pointer</var> variable points to. </p>
<p>Within a string-based parser algorithm that uses a <var>pointer</var> variable, <dfn data-dfn-type="dfn" data-noexport="" id="remaining">remaining<a class="self-link" href="#remaining"></a></dfn> references the substring after <var>pointer</var> in the string
being processed. </p>
<p class="example" id="example-12672b6a"><a class="self-link" href="#example-12672b6a"></a>If "<code>mailto:username@example</code>" is a string being
processed and <var>pointer</var> points to "<code>@</code>", <a data-link-type="dfn" href="#c">c</a> is "<code>@</code>" and <a data-link-type="dfn" href="#remaining">remaining</a> is
"<code>example</code>". </p>
<p>A <dfn data-dfn-type="dfn" data-noexport="" id="syntax-violation">syntax violation<a class="self-link" href="#syntax-violation"></a></dfn> indicates a non-fatal mismatch between input and syntax
requirements. User agents, especially conformance checkers are encouraged to report them
somewhere. </p>
<p class="note no-backref" role="note">A <a data-link-type="dfn" href="#syntax-violation">syntax violation</a> does not mean that the parser
terminates. Termination of a parser is always stated explicitly. E.g., through a return
statement. </p>
<h3 class="heading settled" data-level="1.2" id="percent-encoded-bytes"><span class="secno">1.2. </span><span class="content">Percent-encoded bytes</span><a class="self-link" href="#percent-encoded-bytes"></a></h3>
<p>A <dfn data-dfn-type="dfn" data-noexport="" id="percent-encoded-byte">percent-encoded byte<a class="self-link" href="#percent-encoded-byte"></a></dfn> is "<code>%</code>", followed by two <a data-link-type="dfn" href="#ascii-hex-digits">ASCII hex digits</a>.
Sequences of <a data-link-type="dfn" href="#percent-encoded-byte">percent-encoded bytes</a>, after conversion to bytes,
should not cause <a data-link-type="dfn" href="https://encoding.spec.whatwg.org/#utf-8-decode-without-bom-or-fail">UTF-8 decode without BOM or fail</a> to return failure. </p>
<p>To <dfn data-dfn-type="dfn" data-noexport="" id="percent-encode">percent encode<a class="self-link" href="#percent-encode"></a></dfn> a <var>byte</var> into a <a data-link-type="dfn" href="#percent-encoded-byte">percent-encoded byte</a>, return a string consisting of
"<code>%</code>", followed by a double-digit, uppercase, hexadecimal
representation of <var>byte</var>. </p>
<p>To <dfn data-dfn-type="dfn" data-noexport="" id="percent-decode">percent decode<a class="self-link" href="#percent-decode"></a></dfn> a byte sequence <var>input</var>, run these steps: </p>
<p class="warning">Using anything but <a data-link-type="dfn" href="https://encoding.spec.whatwg.org/#utf-8-decode-without-bom">UTF-8 decode without BOM</a> when the <var>input</var> contains bytes that are not <a data-link-type="dfn" href="https://encoding.spec.whatwg.org/#ascii-byte">ASCII bytes</a> might be insecure and is not recommended. </p>
<ol>
<li>
<p>Let <var>output</var> be an empty byte sequence. </p>
<li>
<p>For each byte <var>byte</var> in <var>input</var>, run these steps: </p>
<ol>
<li>
<p>If <var>byte</var> is not `<code>%</code>`, append <var>byte</var> to <var>output</var>. </p>
<li>
<p>Otherwise, if <var>byte</var> is `<code>%</code>` and the next two
bytes after <var>byte</var> in <var>input</var> are not in the ranges
0x30 to 0x39, 0x41 to 0x46, and 0x61 to 0x66, append <var>byte</var> to <var>output</var>. </p>
<li>
<p>Otherwise, run these substeps: </p>
<ol>
<li>
<p>Let <var>bytePoint</var> be the two bytes after <var>byte</var> in <var>input</var>, <a data-link-type="dfn" href="https://encoding.spec.whatwg.org/#utf-8-decode-without-bom">decoded</a>, and
then interpreted as hexadecimal number. </p>
<li>
<p>Append a byte whose value is <var>bytePoint</var> to <var>output</var>. </p>
<li>
<p>Skip the next two bytes in <var>input</var>. </p>
</ol>
</ol>
<li>
<p>Return <var>output</var>. </p>
</ol>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="simple-encode-set">simple encode set<a class="self-link" href="#simple-encode-set"></a></dfn> are <a data-link-type="dfn" href="#c0-controls">C0 controls</a> and all code points greater
than U+007E. </p>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="default-encode-set">default encode set<a class="self-link" href="#default-encode-set"></a></dfn> is the <a data-link-type="dfn" href="#simple-encode-set">simple encode set</a> and code points U+0020,
'<code>"</code>',
"<code>#</code>",
"<code><</code>",
"<code>></code>",
"<code>?</code>",
"<code>`</code>",
"<code>{</code>",
and
"<code>}</code>". </p>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="userinfo-encode-set">userinfo encode set<a class="self-link" href="#userinfo-encode-set"></a></dfn> is the <a data-link-type="dfn" href="#default-encode-set">default encode set</a> and code points
"<code>/</code>",
"<code>:</code>",
"<code>;</code>",
"<code>=</code>",
"<code>@</code>",
"<code>[</code>",
"<code>\</code>",
"<code>]</code>",
"<code>^</code>",
and
"<code>|</code>". </p>
<p>To <dfn data-dfn-type="dfn" data-noexport="" id="utf-8-percent-encode">UTF-8 percent encode<a class="self-link" href="#utf-8-percent-encode"></a></dfn> a <var>codePoint</var>, using
an <var>encode set</var>, run these steps: </p>
<ol>
<li>
<p>If <var>codePoint</var> is not in <var>encode set</var>, return <var>codePoint</var>. </p>
<li>
<p>Let <var>bytes</var> be the result of running <a data-link-type="dfn" href="https://encoding.spec.whatwg.org/#utf-8-encode">UTF-8 encode</a> on <var>codePoint</var>. </p>
<li>
<p><a data-link-type="dfn" href="#percent-encode">Percent encode</a> each byte in <var>bytes</var>, and then return the results
concatenated, in the same order. </p>
</ol>
<h2 class="heading settled" data-level="2" id="security-considerations"><span class="secno">2. </span><span class="content">Security considerations</span><a class="self-link" href="#security-considerations"></a></h2>
<p>The security of a <a data-link-type="dfn" href="#concept-url">URL</a> is a function of its environment. Care is to be
taken when rendering, interpreting, and passing <a data-link-type="dfn" href="#concept-url">URLs</a> around. </p>
<p>When rendering and allocating new <a data-link-type="dfn" href="#concept-url">URLs</a> "spoofing" needs to be
considered. An attack whereby one <a data-link-type="dfn" href="#concept-host">host</a> or <a data-link-type="dfn" href="#concept-url">URL</a> can be
confused for another. E.g., consider how 1/l/I, m/rn/rri, 0/O, and а/a can all appear
eerily similar. Or worse, consider how U+202A and similar code points are invisible. <a data-link-type="biblio" href="#biblio-uts36">[UTS36]</a> </p>
<p>When passing a <a data-link-type="dfn" href="#concept-url">URL</a> from party <var>A</var> to <var>B</var>, both need to
carefully consider what is happening. <var>A</var> might end up leaking data it does not
want to leak. <var>B</var> might receive input it did not expect and take an action that
harms the user. In particular, <var>B</var> should never trust <var>A</var>, as at some
point <a data-link-type="dfn" href="#concept-url">URLs</a> from <var>A</var> can come from untrusted sources. </p>
<h2 class="heading settled" data-level="3" id="hosts-(domains-and-ip-addresses)"><span class="secno">3. </span><span class="content">Hosts (domains and IP addresses)</span><a class="self-link" href="#hosts-%28domains-and-ip-addresses%29"></a></h2>
<p>A <dfn data-dfn-for="host" data-dfn-type="dfn" data-export="" id="concept-host">host<a class="self-link" href="#concept-host"></a></dfn> is a <a data-link-type="dfn" href="#concept-domain">domain</a>, an <a data-link-type="dfn" href="#concept-ipv4">IPv4 address</a>, or an <a data-link-type="dfn" href="#concept-ipv6">IPv6 address</a>. Typically a <a data-link-type="dfn" href="#concept-host">host</a> serves as a network address, but it is sometimes (ab)used as opaque
identifier in <a data-link-type="dfn" href="#concept-url">URLs</a> where a network address is not necessary. </p>
<p>A <dfn data-dfn-for="host" data-dfn-type="dfn" data-export="" id="concept-domain">domain<a class="self-link" href="#concept-domain"></a></dfn> identifies a realm within a
network. <a data-link-type="biblio" href="#biblio-rfc1034">[RFC1034]</a> </p>
<p>An <dfn data-dfn-for="host" data-dfn-type="dfn" data-export="" id="concept-ipv4">IPv4 address<a class="self-link" href="#concept-ipv4"></a></dfn> is a 32-bit identifier. <a data-link-type="biblio" href="#biblio-rfc791">[RFC791]</a> </p>
<p>An <dfn data-dfn-for="host" data-dfn-type="dfn" data-export="" id="concept-ipv6">IPv6 address<a class="self-link" href="#concept-ipv6"></a></dfn> is a 128-bit identifier and
for the purposes of this specification represented as an ordered list of
eight <dfn data-dfn-type="dfn" data-lt="IPv6 piece" data-noexport="" id="concept-ipv6-piece">16-bit pieces<a class="self-link" href="#concept-ipv6-piece"></a></dfn>. <a data-link-type="biblio" href="#biblio-rfc4291">[RFC4291]</a> </p>
<p class="note" role="note">Support for <code><zone_id></code> is <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=27234#c2">intentionally omitted</a>. </p>
<h3 class="heading settled" data-level="3.1" id="idna"><span class="secno">3.1. </span><span class="content">IDNA</span><a class="self-link" href="#idna"></a></h3>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="concept-domain-to-ascii">domain to ASCII<a class="self-link" href="#concept-domain-to-ascii"></a></dfn> given a <a data-link-type="dfn" href="#concept-domain">domain</a> <var>domain</var>, runs these steps: </p>
<ol>
<li>
<p>Let <var>result</var> be the result of running <a data-link-type="dfn" href="http://www.unicode.org/reports/tr46/#ToASCII">Unicode ToASCII</a> with <i>domain_name</i> set to <var>domain</var>, <i>UseSTD3ASCIIRules</i> set to false, <i>processing_option</i> set to <i>Transitional_Processing</i>, and <i>VerifyDnsLength</i> set to false. </p>
<li>
<p>If <var>result</var> is a failure value, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>, return failure. </p>
<li>
<p>Return <var>result</var>. </p>
</ol>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="concept-domain-to-unicode">domain to Unicode<a class="self-link" href="#concept-domain-to-unicode"></a></dfn> given a <a data-link-type="dfn" href="#concept-domain">domain</a> <var>domain</var>, runs these steps: </p>
<ol>
<li>
<p>Let <var>result</var> be the result of running <a data-link-type="dfn" href="http://www.unicode.org/reports/tr46/#ToUnicode">Unicode ToUnicode</a> with <i>domain_name</i> set to <var>domain</var>, <i>UseSTD3ASCIIRules</i> set to false. </p>
<li>
<p>Signify <a data-link-type="dfn" href="#syntax-violation">syntax violations</a> for any returned errors, and then, return <var>result</var>. </p>
</ol>
<h3 class="heading settled" data-level="3.2" id="host-syntax"><span class="secno">3.2. </span><span class="content">Host syntax</span><a class="self-link" href="#host-syntax"></a></h3>
<p>A <dfn data-dfn-for="hostsyntax" data-dfn-type="dfn" data-export="" id="syntax-host">host<a class="self-link" href="#syntax-host"></a></dfn> must be a <a data-link-type="dfn" href="#syntax-host-domain">domain</a>, an <a data-link-type="dfn" href="#syntax-host-ipv4">IPv4 address</a>, or "<code>[</code>",
followed by an <a data-link-type="dfn" href="#syntax-host-ipv6">IPv6 address</a>, followed by "<code>]</code>". </p>
<p>A <var>domain</var> is a <dfn data-dfn-type="dfn" data-noexport="" id="valid-domain">valid domain<a class="self-link" href="#valid-domain"></a></dfn> if these steps return success: </p>
<ol>
<li>
<p>Let <var>result</var> be the result of running <a data-link-type="dfn" href="http://www.unicode.org/reports/tr46/#ToASCII">Unicode ToASCII</a> with <i>domain_name</i> set to <var>domain</var>, <i>UseSTD3ASCIIRules</i> set to true, <i>processing_option</i> set to <i>Nontransitional_Processing</i>, and <i>VerifyDnsLength</i> set to true. </p>
<li>
<p>If <var>result</var> is a failure value, return failure. </p>
<li>
<p>Set <var>result</var> to the result of running <a data-link-type="dfn" href="http://www.unicode.org/reports/tr46/#ToUnicode">Unicode ToUnicode</a> with <i>domain_name</i> set to <var>result</var>, <i>UseSTD3ASCIIRules</i> set to true. </p>
<li>
<p>If <var>result</var> contains any errors, return failure. </p>
<li>
<p>Return success. </p>
</ol>
<p class="XXX">Ideally we define this in terms of a sequence of code points that make up a <a data-link-type="dfn" href="#valid-domain">valid domain</a> rather than through a whack-a-mole: <a href="https://www.w3.org/Bugs/Public/show_bug.cgi?id=25334">bug 25334</a>. </p>
<p>A <dfn data-dfn-for="hostsyntax" data-dfn-type="dfn" data-export="" id="syntax-host-domain">domain<a class="self-link" href="#syntax-host-domain"></a></dfn> must be a string that
is a <a data-link-type="dfn" href="#valid-domain">valid domain</a>. </p>
<p>An <dfn data-dfn-for="hostsyntax" data-dfn-type="dfn" data-export="" id="syntax-host-ipv4">IPv4 address<a class="self-link" href="#syntax-host-ipv4"></a></dfn> must be four
sequences of up to three <a data-link-type="dfn" href="#ascii-digits">ASCII digits</a> per sequence, each representing a decimal
number no greater than 255, and separated from each other by "<code>.</code>". </p>
<p>An <dfn data-dfn-for="hostsyntax" data-dfn-type="dfn" data-export="" id="syntax-host-ipv6">IPv6 address<a class="self-link" href="#syntax-host-ipv6"></a></dfn> is defined in the <a href="https://tools.ietf.org/html/rfc4291#section-2.2">"Text Representation of Addresses" chapter of IP Version 6 Addressing Architecture</a>. <a data-link-type="biblio" href="#biblio-rfc4291">[RFC4291]</a> </p>
<h3 class="heading settled" data-level="3.3" id="host-parsing"><span class="secno">3.3. </span><span class="content">Host parsing</span><a class="self-link" href="#host-parsing"></a></h3>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="concept-host-parser">host parser<a class="self-link" href="#concept-host-parser"></a></dfn> takes a string <var>input</var> and
an optional <var>Unicode flag</var> (unset unless stated otherwise), and then runs these
steps: </p>
<ol>
<li>
<p>If <var>input</var> starts with "<code>[</code>", run these
substeps: </p>
<ol>
<li>
<p>If <var>input</var> does not end with
"<code>]</code>", <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>, return failure. </p>
<li>
<p>Return the result of <a data-link-type="dfn" href="#concept-ipv6-parser">IPv6 parsing</a> <var>input</var> with its leading "<code>[</code>" and trailing
"<code>]</code>" removed. </p>
</ol>
<li>
<p>Let <var>domain</var> be the result of <a data-link-type="dfn" href="https://encoding.spec.whatwg.org/#utf-8-decode-without-bom">UTF-8 decode without BOM</a> on the <a data-link-type="dfn" href="#percent-decode">percent decoding</a> of <a data-link-type="dfn" href="https://encoding.spec.whatwg.org/#utf-8-encode">UTF-8 encode</a> on <var>input</var>. </p>
<li>
<p>Let <var>asciiDomain</var> be the result of running <a data-link-type="dfn" href="#concept-domain-to-ascii">domain to ASCII</a> on <var>domain</var>. </p>
<li>
<p>If <var>asciiDomain</var> is failure, return failure. </p>
<li>
<p>If <var>asciiDomain</var> contains
U+0000,
U+0009,
U+000A,
U+000D,
U+0020,
"<code>#</code>",
"<code>%</code>",
"<code>/</code>",
"<code>:</code>",
"<code>?</code>",
"<code>@</code>",
"<code>[</code>",
"<code>\</code>",
or
"<code>]</code>", <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>, return failure. </p>
<li>
<p>Let <var>ipv4Host</var> be the result of <a data-link-type="dfn" href="#concept-ipv4-parser">IPv4 parsing</a> <var>asciiDomain</var>. </p>
<li>
<p>If <var>ipv4Host</var> is an <a data-link-type="dfn" href="#concept-ipv4">IPv4 address</a> or failure, return <var>ipv4Host</var>. </p>
<li>
<p>Return <var>asciiDomain</var> if the <var>Unicode flag</var> is unset, and the
result of running <a data-link-type="dfn" href="#concept-domain-to-unicode">domain to Unicode</a> on <var>asciiDomain</var> otherwise. </p>
</ol>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="ipv4-number-parser">IPv4 number parser<a class="self-link" href="#ipv4-number-parser"></a></dfn> takes a string <var>input</var> and a <var>syntaxViolationFlag</var> pointer, and then runs these steps:</p>
<ol>
<li>
<p>Let <var>R</var> be 10. </p>
<li>
<p>If <var>input</var> contains at least two code points and the first two code points
are either "<code>0x</code>" or "<code>0X</code>", run these substeps: </p>
<ol>
<li>
<p>Set <var>syntaxViolationFlag</var>. </p>
<li>
<p>Remove the first two code points from <var>input</var>. </p>
<li>
<p>Set <var>R</var> to 16. </p>
</ol>
<li>
<p>If <var>input</var> is the empty string, return zero. </p>
<li>
<p>Otherwise, if <var>input</var> contains at least two code points and the first code
point is "<code>0</code>", run these substeps: </p>
<ol>
<li>
<p>Set <var>syntaxViolationFlag</var>. </p>
<li>
<p>Remove the first code point from <var>input</var>. </p>
<li>
<p>Set <var>R</var> to 8. </p>
</ol>
<li>
<p>If <var>input</var> contains a code point that is not a radix-<var>R</var> digit,
and return failure. </p>
<li>
<p>Return the mathematical integer value that is represented by <var>input</var> in
radix-<var>R</var> notation, using <a data-link-type="dfn" href="#ascii-hex-digits">ASCII hex digits</a> for digits with values 0
through 15. </p>
</ol>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="concept-ipv4-parser">IPv4 parser<a class="self-link" href="#concept-ipv4-parser"></a></dfn> takes a string <var>input</var> and then
runs these steps:</p>
<ol>
<li>
<p>Let <var>syntaxViolationFlag</var> be unset. </p>
<li>
<p>Let <var>parts</var> be <var>input</var> split on "<code>.</code>". </p>
<li>
<p>If the last item in <var>parts</var> is the empty string, set <var>syntaxViolationFlag</var> and remove the last item from <var>parts</var>. </p>
<li>
<p>If <var>parts</var> has more than four items, return <var>input</var>. </p>
<li>
<p>Let <var>numbers</var> be the empty list. </p>
<li>
<p>For each <var>part</var> in <var>parts</var>: </p>
<ol>
<li>
<p>If <var>part</var> is the empty string, return <var>input</var>. </p>
<p class="example no-backref" id="example-c2afe535"><a class="self-link" href="#example-c2afe535"></a><code>0..0x300</code> is a <a data-link-type="dfn" href="#concept-domain">domain</a>, not
an <a data-link-type="dfn" href="#concept-ipv4">IPv4 address</a>. </p>
<li>
<p>Let <var>n</var> be the result of <a data-link-type="dfn" href="#ipv4-number-parser">parsing</a> <var>part</var> using <var>syntaxViolationFlag</var>. </p>
<li>
<p>If <var>n</var> is failure, return <var>input</var>. </p>
<li>
<p>Append <var>n</var> to <var>numbers</var>. </p>
</ol>
<li>
<p>If <var>syntaxViolationFlag</var> is set, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>. </p>
<li>
<p>If any item in <var>numbers</var> is greater than 255, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>. </p>
<li>
<p>If any but the last item in <var>numbers</var> is greater than 255, return
failure. </p>
<li>
<p>If the last item in <var>numbers</var> is greater than or equal to
256<sup>(5 − the number of items in <var>numbers</var>)</sup>, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>, return failure. </p>
<li>
<p>Let <var>ipv4</var> be the last item in <var>numbers</var>. </p>
<li>
<p>Remove the last item from <var>numbers</var>. </p>
<li>
<p>Let <var>counter</var> be zero. </p>
<li>
<p>For each <var>n</var> in <var>numbers</var>: </p>
<ol>
<li>
<p>Increment <var>ipv4</var> by <var>n</var> ×
256<sup>(3 − <var>counter</var>)</sup>. </p>
<li>
<p>Increment <var>counter</var> by one. </p>
</ol>
<li>
<p>Return <var>ipv4</var>. </p>
</ol>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="concept-ipv6-parser">IPv6 parser<a class="self-link" href="#concept-ipv6-parser"></a></dfn> takes a string <var>input</var> and
then runs these steps: </p>
<ol>
<li>
<p>Let <var>address</var> be a new <a data-link-type="dfn" href="#concept-ipv6">IPv6 address</a> with its <a data-link-type="dfn" href="#concept-ipv6-piece">16-bit pieces</a> initialized to 0. </p>
<li>
<p>Let <var>piece pointer</var> be a pointer into <var>address</var>’s <a data-link-type="dfn" href="#concept-ipv6-piece">16-bit pieces</a>, initially zero
(pointing to the first <a data-link-type="dfn" href="#concept-ipv6-piece">16-bit piece</a>),
and let <var>piece</var> be the <a data-link-type="dfn" href="#concept-ipv6-piece">16-bit piece</a> it points to. </p>
<li>
<p>Let <var>compress pointer</var> be another pointer into <var>address</var>’s <a data-link-type="dfn" href="#concept-ipv6-piece">16-bit pieces</a>, initially
null and pointing to nothing. </p>
<li>
<p>Let <var>pointer</var> be a pointer into <var>input</var>, initially zero (pointing to the first code point). </p>
<li>
<p>If <a data-link-type="dfn" href="#c">c</a> is "<code>:</code>", run these substeps: </p>
<ol>
<li>
<p>If <a data-link-type="dfn" href="#remaining">remaining</a> does not start with "<code>:</code>", <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>, return failure. </p>
<li>
<p>Increase <var>pointer</var> by two. </p>
<li>
<p>Increase <var>piece pointer</var> by one and then set <var>compress pointer</var> to <var>piece pointer</var>. </p>
</ol>
<li>
<p><dfn data-dfn-type="dfn" data-lt="IPv6 parser Main" data-noexport="" id="concept-ipv6-parser-main">Main<a class="self-link" href="#concept-ipv6-parser-main"></a></dfn>:
While <a data-link-type="dfn" href="#c">c</a> is not the <a data-link-type="dfn" href="#eof-code-point">EOF code point</a>, run these
substeps: </p>
<ol>
<li>
<p>If <var>piece pointer</var> is eight, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>, return failure. </p>
<li>
<p>If <a data-link-type="dfn" href="#c">c</a> is "<code>:</code>", run these inner
substeps: </p>
<ol>
<li>
<p>If <var>compress pointer</var> is non-null, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>,
return failure. </p>
<li>Increase <var>pointer</var> and <var>piece pointer</var> by one, set <var>compress pointer</var> to <var>piece pointer</var>,
and then jump to <a data-link-type="dfn" href="#concept-ipv6-parser-main">Main</a>.
</ol>
<li>
<p>Let <var>value</var> and <var>length</var> be 0. </p>
<li>
<p>While <var>length</var> is less than 4 and <a data-link-type="dfn" href="#c">c</a> is an <a data-link-type="dfn" href="#ascii-hex-digits">ASCII hex digit</a>, set <var>value</var> to <var>value</var> × 0x10 + <a data-link-type="dfn" href="#c">c</a> interpreted as hexadecimal number,
and increase <var>pointer</var> and <var>length</var> by one. </p>
<li>
<p>Switching on <a data-link-type="dfn" href="#c">c</a>: </p>
<dl class="switch">
<dt>"<code>.</code>"
<dd>
<ol>
<li>
<p>If <var>length</var> is 0, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>, return failure. </p>
<li>
<p>Decrease <var>pointer</var> by <var>length</var>. </p>
<li>
<p>Jump to <a data-link-type="dfn" href="#concept-ipv6-parser-ipv4">IPv4</a>. </p>
</ol>
<dt>"<code>:</code>"
<dd>
<ol>
<li>
<p>Increase <var>pointer</var> by one. </p>
<li>
<p>If <a data-link-type="dfn" href="#c">c</a> is the <a data-link-type="dfn" href="#eof-code-point">EOF code point</a>, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>,
return failure. </p>
</ol>
<dt>Anything but the <a data-link-type="dfn" href="#eof-code-point">EOF code point</a>
<dd>
<p><a data-link-type="dfn" href="#syntax-violation">Syntax violation</a>, return failure. </p>
</dl>
<li>
<p>Set <var>piece</var> to <var>value</var>. </p>
<li>
<p>Increase <var>piece pointer</var> by one. </p>
</ol>
<li>
<p>If <a data-link-type="dfn" href="#c">c</a> is the <a data-link-type="dfn" href="#eof-code-point">EOF code point</a>, jump to <a data-link-type="dfn" href="#concept-ipv6-parser-finale">Finale</a>. </p>
<li>
<p><dfn data-dfn-type="dfn" data-lt="IPv6 parser IPv4" data-noexport="" id="concept-ipv6-parser-ipv4">IPv4<a class="self-link" href="#concept-ipv6-parser-ipv4"></a></dfn>:
If <var>piece pointer</var> is greater than six, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>, return failure. </p>
<li>
<p>Let <var>dots seen</var> be 0. </p>
<li>
<p>While <a data-link-type="dfn" href="#c">c</a> is not the <a data-link-type="dfn" href="#eof-code-point">EOF code point</a>, run
these substeps: </p>
<ol>
<li>
<p>Let <var>value</var> be null. </p>
<li>
<p>If <a data-link-type="dfn" href="#c">c</a> is not an <a data-link-type="dfn" href="#ascii-digits">ASCII digit</a>, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>,
return failure. </p>
<li>
<p>While <a data-link-type="dfn" href="#c">c</a> is an <a data-link-type="dfn" href="#ascii-digits">ASCII digit</a>, run these subsubsteps: </p>
<ol>
<li>
<p>Let <var>number</var> be <a data-link-type="dfn" href="#c">c</a> interpreted as decimal number. </p>
<li>
<p>If <var>value</var> is null, set <var>value</var> to <var>number</var>. </p>
<p>Otherwise, if <var>value</var> is 0, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>, return failure. </p>
<p>Otherwise, set <var>value</var> to <var>value</var> × 10 + <var>number</var>. </p>
<li>
<p>Increase <var>pointer</var> by one. </p>
<li>
<p>If <var>value</var> is greater than 255, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>,
return failure. </p>
</ol>
<li>
<p>If <var>dots seen</var> is less than 3 and <a data-link-type="dfn" href="#c">c</a> is not a "<code>.</code>", <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>, return failure. </p>
<li>
<p>Set <var>piece</var> to <var>piece</var> × 0x100 + <var>value</var>. </p>
<li>
<p>If <var>dots seen</var> is 1 or 3, increase <var>piece pointer</var> by one. </p>
<li>
<p>If <a data-link-type="dfn" href="#c">c</a> is not the <a data-link-type="dfn" href="#eof-code-point">EOF code point</a>, increase <var>pointer</var> by
one. </p>
<li>
<p>If <var>dots seen</var> is 3 and <a data-link-type="dfn" href="#c">c</a> is not
the <a data-link-type="dfn" href="#eof-code-point">EOF code point</a>, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>, return failure. </p>
<li>
<p>Increase <var>dots seen</var> by one. </p>
</ol>
<li>
<p><dfn data-dfn-type="dfn" data-lt="IPv6 parser Finale" data-noexport="" id="concept-ipv6-parser-finale">Finale<a class="self-link" href="#concept-ipv6-parser-finale"></a></dfn>:
If <var>compress pointer</var> is non-null, run these substeps: </p>
<ol>
<li>
<p>Let <var>swaps</var> be <var>piece pointer</var> − <var>compress pointer</var>. </p>
<li>
<p>Set <var>piece pointer</var> to seven. </p>
<li>
<p>While <var>piece pointer</var> is not zero and <var>swaps</var> is
greater than zero, swap <var>piece</var> with the <a data-link-type="dfn" href="#concept-ipv6-piece">piece</a> at pointer <var>compress pointer</var> + <var>swaps</var> − 1, and then
decrease both <var>piece pointer</var> and <var>swaps</var> by one. </p>
</ol>
<li>
<p>Otherwise, if <var>compress pointer</var> is null and <var>piece pointer</var> is
not eight, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>, return failure. </p>
<li>
<p>Return <var>address</var>. </p>
</ol>
<p class="note no-backref" role="note">To be clear, <a data-link-type="dfn" href="#concept-ipv6-parser-main">Main</a>, <a data-link-type="dfn" href="#concept-ipv6-parser-ipv4">IPv4</a>, and <a data-link-type="dfn" href="#concept-ipv6-parser-finale">Finale</a> are simple markers.
They serve no purpose other than being a location the algorithm can jump to. </p>
<h3 class="heading settled" data-level="3.4" id="host-serializing"><span class="secno">3.4. </span><span class="content">Host serializing</span><a class="self-link" href="#host-serializing"></a></h3>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="concept-host-serializer">host serializer<a class="self-link" href="#concept-host-serializer"></a></dfn> takes a <a data-link-type="dfn" href="#concept-host">host</a> <var>host</var> and then runs these steps: </p>
<ol>
<li>
<p>If <var>host</var> is an <a data-link-type="dfn" href="#concept-ipv4">IPv4 address</a>, return the result of
running the <a data-link-type="dfn" href="#concept-ipv4-serializer">IPv4 serializer</a> on <var>host</var>. </p>
<li>
<p>Otherwise, if <var>host</var> is an <a data-link-type="dfn" href="#concept-ipv6">IPv6 address</a>, return
"<code>[</code>", followed by the result of running the <a data-link-type="dfn" href="#concept-ipv6-serializer">IPv6 serializer</a> on <var>host</var>,
followed by "<code>]</code>". </p>
<li>
<p>Otherwise, <var>host</var> is a <a data-link-type="dfn" href="#concept-domain">domain</a>, return <var>host</var>. </p>
</ol>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="concept-ipv4-serializer">IPv4 serializer<a class="self-link" href="#concept-ipv4-serializer"></a></dfn> takes an <a data-link-type="dfn" href="#concept-ipv4">IPv4 address</a> <var>address</var> and then runs these steps:</p>
<ol>
<li>
<p>Let <var>output</var> be the empty string. </p>
<li>
<p>Let <var>n</var> be the value of <var>address</var>. </p>
<li>
<p>Repeat four times: </p>
<ol>
<li>
<p>Prepend <var>n</var> % 256, <a data-link-type="dfn" href="#serialize-an-integer">serialized</a>, to <var>output</var>. </p>
<li>
<p>Unless this is the fourth time, prepend "<code>.</code>" to <var>output</var>. </p>
<li>
<p>Set <var>n</var> to floor(<var>n</var> / 256). </p>
</ol>
<li>
<p>Return <var>output</var>. </p>
</ol>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="concept-ipv6-serializer">IPv6 serializer<a class="self-link" href="#concept-ipv6-serializer"></a></dfn> takes an <a data-link-type="dfn" href="#concept-ipv6">IPv6 address</a> <var>address</var> and then runs these steps: </p>
<ol>
<li>
<p>Let <var>output</var> be the empty string. </p>
<li>
<p>Let <var>compress pointer</var> be a pointer to the first <a data-link-type="dfn" href="#concept-ipv6-piece">16-bit piece</a> in the first longest
sequences of <var>address</var>’s <a data-link-type="dfn" href="#concept-ipv6-piece">16-bit pieces</a> that are 0. </p>
<p class="example" id="example-e2b3492e"><a class="self-link" href="#example-e2b3492e"></a>In <code>0:f:0:0:f:f:0:0</code> it would point to
the second 0. </p>
<li>
<p>If there is no sequence of <var>address</var>’s <a data-link-type="dfn" href="#concept-ipv6-piece">16-bit pieces</a> that are 0 longer than
one, set <var>compress pointer</var> to null. </p>
<li>
<p>For each <var>piece</var> in <var>address</var>’s <a data-link-type="dfn" href="#concept-ipv6-piece">pieces</a>, run these substeps: </p>
<ol>
<li>
<p>If <var>compress pointer</var> points to <var>piece</var>, append "<code>::</code>" to <var>output</var> if <var>piece</var> is <var>address</var>’s first <a data-link-type="dfn" href="#concept-ipv6-piece">piece</a> and append
"<code>:</code>" otherwise, and then run these substeps again with all
subsequent <a data-link-type="dfn" href="#concept-ipv6-piece">pieces</a> in <var>address</var>’s <a data-link-type="dfn" href="#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 data-link-type="dfn" href="#concept-ipv6-piece">pieces</a>. </p>
<li>
<p>Append <var>piece</var>, represented as the shortest
possible lowercase hexadecimal number, to <var>output</var>. </p>
<li>
<p>If <var>piece</var> is not <var>address</var>’s last <a data-link-type="dfn" href="#concept-ipv6-piece">piece</a>,
append "<code>:</code>" to <var>output</var>. </p>
</ol>
<li>
<p>Return <var>output</var>. </p>
</ol>
<p class="note" role="note">This algorithm requires the recommendation from
A Recommendation for IPv6 Address Text Representation. <a data-link-type="biblio" href="#biblio-rfc5952">[RFC5952]</a> </p>
<h3 class="heading settled" data-level="3.5" id="host-equivalence"><span class="secno">3.5. </span><span class="content">Host equivalence</span><a class="self-link" href="#host-equivalence"></a></h3>
<p>To determine whether a <a data-link-type="dfn" href="#concept-host">host</a> <var>A</var> <dfn data-dfn-for="host" data-dfn-type="dfn" data-export="" id="concept-host-equals">equals<a class="self-link" href="#concept-host-equals"></a></dfn> <var>B</var>, return true if <var>A</var> is <var>B</var>, and false otherwise.</p>
<p class="XXX">Certificate comparison requires a host equivalence check that ignores the
trailing dot of a domain (if any). However, those hosts have also various other facets
enforced, such as DNS length, that are not enforced here, as URLs do not enforce them. If
anyone has a good suggestion for how to bring these two closer together, or what a good
unified model would be, please file an issue. </p>
<h2 class="heading settled" data-level="4" id="urls"><span class="secno">4. </span><span class="content">URLs</span><a class="self-link" href="#urls"></a></h2>
<p>A <dfn data-dfn-for="url" data-dfn-type="dfn" data-export="" data-lt="URL|URL record" id="concept-url">URL<a class="self-link" href="#concept-url"></a></dfn> is a universal
identifier. To disambiguate from a <a data-link-type="dfn" href="#syntax-url">URL string</a> it can also be referred to as a <a data-link-type="dfn" href="#concept-url">URL record</a>. </p>
<p>A <a data-link-type="dfn" href="#concept-url">URL</a>’s <dfn data-dfn-for="url" data-dfn-type="dfn" data-export="" id="concept-url-scheme">scheme<a class="self-link" href="#concept-url-scheme"></a></dfn> is an <a data-link-type="dfn" href="#ascii-string">ASCII string</a> that identifies the type of <a data-link-type="dfn" href="#concept-url">URL</a> and can be used to
dispatch a <a data-link-type="dfn" href="#concept-url">URL</a> for further processing after <a data-link-type="dfn" href="#concept-url-parser">parsing</a>.
It is initially the empty string. </p>
<p>A <a data-link-type="dfn" href="#concept-url">URL</a>’s <dfn data-dfn-for="url" data-dfn-type="dfn" data-export="" id="concept-url-username">username<a class="self-link" href="#concept-url-username"></a></dfn> is
an <a data-link-type="dfn" href="#ascii-string">ASCII string</a> identifying a user. It is initially the empty string. </p>
<p>A <a data-link-type="dfn" href="#concept-url">URL</a>’s <dfn data-dfn-for="url" data-dfn-type="dfn" data-export="" id="concept-url-password">password<a class="self-link" href="#concept-url-password"></a></dfn> is
either null or an <a data-link-type="dfn" href="#ascii-string">ASCII string</a> identifying a user’s credentials. It is initially
null. </p>
<p>A <a data-link-type="dfn" href="#concept-url">URL</a>’s <dfn data-dfn-for="url" data-dfn-type="dfn" data-export="" id="concept-url-host">host<a class="self-link" href="#concept-url-host"></a></dfn> is either
null or a <a data-link-type="dfn" href="#concept-host">host</a>. It is initially null. </p>
<p>A <a data-link-type="dfn" href="#concept-url">URL</a>’s <dfn data-dfn-for="url" data-dfn-type="dfn" data-export="" id="concept-url-port">port<a class="self-link" href="#concept-url-port"></a></dfn> is either
null or a 16-bit unsigned integer that identifies a networking port. It is initially null. </p>
<p>A <a data-link-type="dfn" href="#concept-url">URL</a>’s <dfn data-dfn-for="url" data-dfn-type="dfn" data-export="" id="concept-url-path">path<a class="self-link" href="#concept-url-path"></a></dfn> is a list of
zero or more <a data-link-type="dfn" href="#ascii-string">ASCII string</a> holding data, usually identifying a location in
hierarchical form. It is initially the empty list. </p>
<p>A <a data-link-type="dfn" href="#concept-url">URL</a>’s <dfn data-dfn-for="url" data-dfn-type="dfn" data-export="" id="concept-url-query">query<a class="self-link" href="#concept-url-query"></a></dfn> is either
null or an <a data-link-type="dfn" href="#ascii-string">ASCII string</a> holding data. It is initially null. </p>
<p>A <a data-link-type="dfn" href="#concept-url">URL</a>’s <dfn data-dfn-for="url" data-dfn-type="dfn" data-export="" id="concept-url-fragment">fragment<a class="self-link" href="#concept-url-fragment"></a></dfn> is
either null or a string holding data that can be used for further processing on the
resource the <a data-link-type="dfn" href="#concept-url">URL</a>’s other components identify. It is initially null. </p>
<p class="note no-backref" role="note">This is not an <a data-link-type="dfn" href="#ascii-string">ASCII string</a> on purpose. </p>
<p id="non-relative-flag">A <a data-link-type="dfn" href="#concept-url">URL</a> also has an associated <dfn data-dfn-for="url" data-dfn-type="dfn" data-export="" id="url-cannot-be-a-base-url-flag">cannot-be-a-base-URL flag<a class="self-link" href="#url-cannot-be-a-base-url-flag"></a></dfn>. It is initially unset. </p>
<p>A <a data-link-type="dfn" href="#concept-url">URL</a> also has an associated <dfn data-dfn-for="url" data-dfn-type="dfn" data-export="" id="concept-url-object">object<a class="self-link" href="#concept-url-object"></a></dfn> that is null, a <code class="idl"><a data-link-type="idl" href="https://w3c.github.io/FileAPI/#dfn-Blob">Blob</a></code> object, a <code class="idl"><a data-link-type="idl" href="https://w3c.github.io/media-source/#idl-def-MediaSource">MediaSource</a></code> object, or a <code class="idl"><a data-link-type="idl" href="https://www.w3.org/TR/mediacapture-streams/#idl-def-MediaStream">MediaStream</a></code> object. It is initially null. <a data-link-type="biblio" href="#biblio-fileapi">[FILEAPI]</a> <a data-link-type="biblio" href="#biblio-media-source">[MEDIA-SOURCE]</a> <a data-link-type="biblio" href="#biblio-mediacapture-streams">[MEDIACAPTURE-STREAMS]</a> </p>
<p class="note no-backref" role="note">At this point this is used primarily to support
"<code>blob</code>" <a data-link-type="dfn" href="#concept-url">URLs</a>, but others can be added going forward, hence
"object". </p>
<hr>
<p>A <dfn data-dfn-type="dfn" data-export="" id="special-scheme">special scheme<a class="self-link" href="#special-scheme"></a></dfn> is a <a data-link-type="dfn" href="#concept-url-scheme">scheme</a> listed in the first column of
the following table. A <dfn data-dfn-type="dfn" data-noexport="" id="default-port">default port<a class="self-link" href="#default-port"></a></dfn> is a <a data-link-type="dfn" href="#special-scheme">special scheme</a>’s optional
corresponding <a data-link-type="dfn" href="#concept-url-port">port</a> and is listed in the second column on the same row. </p>
<table>
<tbody>
<tr>
<th><a data-link-type="dfn" href="#concept-url-scheme">scheme</a>
<th><a data-link-type="dfn" href="#concept-url-port">port</a>
<tr>
<td>"<code>ftp</code>"
<td>21
<tr>
<td>"<code>file</code>"
<td>
<tr>
<td>"<code>gopher</code>"
<td>70
<tr>
<td>"<code>http</code>"
<td>80
<tr>
<td>"<code>https</code>"
<td>443
<tr>
<td>"<code>ws</code>"
<td>80
<tr>
<td>"<code>wss</code>"
<td>443
</table>
<p>A <a data-link-type="dfn" href="#concept-url">URL</a> <dfn data-dfn-type="dfn" data-export="" id="is-special">is special<a class="self-link" href="#is-special"></a></dfn> if its <a data-link-type="dfn" href="#concept-url-scheme">scheme</a> is a <a data-link-type="dfn" href="#special-scheme">special scheme</a>. </p>
<p>A <dfn data-dfn-type="dfn" data-export="" id="local-scheme">local scheme<a class="self-link" href="#local-scheme"></a></dfn> is a <a data-link-type="dfn" href="#concept-url-scheme">scheme</a> that is "<code>about</code>",
"<code>blob</code>", "<code>data</code>", or "<code>filesystem</code>". </p>
<p>A <a data-link-type="dfn" href="#concept-url">URL</a> <dfn data-dfn-type="dfn" data-noexport="" id="is-local">is local<a class="self-link" href="#is-local"></a></dfn> if its <a data-link-type="dfn" href="#concept-url-scheme">scheme</a> is a <a data-link-type="dfn" href="#local-scheme">local scheme</a>. </p>
<p class="note" role="note">This definition is used externally. E.g., by the Fetch Standard and
Referrer Policy. <a data-link-type="biblio" href="#biblio-fetch">[FETCH]</a> <a data-link-type="biblio" href="#biblio-referrer-policy">[REFERRER-POLICY]</a> </p>
<p>An <dfn data-dfn-type="dfn" data-export="" id="http-scheme">HTTP(S) scheme<a class="self-link" href="#http-scheme"></a></dfn> is a <a data-link-type="dfn" href="#concept-url-scheme">scheme</a> that is
"<code>http</code>" or "<code>https</code>". </p>
<p>A <dfn data-dfn-type="dfn" data-export="" id="network-scheme">network scheme<a class="self-link" href="#network-scheme"></a></dfn> is a <a data-link-type="dfn" href="#concept-url-scheme">scheme</a> that is "<code>ftp</code>" or an <span>HTTP(S) scheme</span>. </p>
<p>A <dfn data-dfn-type="dfn" data-export="" id="fetch-scheme">fetch scheme<a class="self-link" href="#fetch-scheme"></a></dfn> is a <a data-link-type="dfn" href="#concept-url-scheme">scheme</a> that is "<code>about</code>",
"<code>blob</code>", "<code>data</code>", "<code>file</code>", "<code>filesystem</code>", or a <span>network scheme</span>. </p>
<p class="note no-backref" role="note"><a data-link-type="dfn" href="#http-scheme">HTTP(S) scheme</a>, <a data-link-type="dfn" href="#network-scheme">network scheme</a>, and <span>fetch scheme</span> are used by HTML. <a data-link-type="biblio" href="#biblio-html">[HTML]</a> </p>
<p>A <a data-link-type="dfn" href="#concept-url">URL</a> <dfn data-dfn-type="dfn" data-lt="include credentials" data-noexport="" id="include-credentials">includes credentials<a class="self-link" href="#include-credentials"></a></dfn> if either
its <a data-link-type="dfn" href="#concept-url-username">username</a> is not the empty string or its <a data-link-type="dfn" href="#concept-url-password">password</a> is
non-null. </p>
<p>A <a data-link-type="dfn" href="#concept-url">URL</a> can be designated as <dfn data-dfn-type="dfn" data-noexport="" id="concept-base-url">base URL<a class="self-link" href="#concept-base-url"></a></dfn>. </p>
<p class="note no-backref" role="note">A <a data-link-type="dfn" href="#concept-base-url">base URL</a> is useful for the <a data-link-type="dfn" href="#concept-url-parser">URL parser</a> when the
input might be a <a data-link-type="dfn" href="#syntax-url-relative">relative URL</a>. </p>
<hr>
<p>To <dfn data-dfn-type="dfn" data-local-lt="pop" data-noexport="" id="pop-a-urls-path">pop a <var>url</var>’s path<a class="self-link" href="#pop-a-urls-path"></a></dfn>, if <var>url</var>’s <a data-link-type="dfn" href="#concept-url-scheme">scheme</a> is not "<code>file</code>" or <var>url</var>’s <a data-link-type="dfn" href="#concept-url-path">path</a> does not contain a single string that is a <a data-link-type="dfn" href="#normalized-windows-drive-letter">normalized Windows drive letter</a>, remove <var>url</var>’s <a data-link-type="dfn" href="#concept-url-path">path</a>’s
last string, if any. </p>
<h3 class="heading settled" data-level="4.1" id="url-syntax"><span class="secno">4.1. </span><span class="content">URL syntax</span><a class="self-link" href="#url-syntax"></a></h3>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" data-lt="URL|URL string" id="syntax-url">URL<a class="self-link" href="#syntax-url"></a></dfn> must be either
a <a data-link-type="dfn" href="#syntax-url-relative-with-fragment">relative URL with fragment</a> or an <a data-link-type="dfn" href="#syntax-url-absolute-with-fragment">absolute URL with fragment</a>. To
disambiguate from a <a data-link-type="dfn" href="#concept-url">URL record</a> it can also be referred to as a <a data-link-type="dfn" href="#syntax-url">URL string</a>. </p>
<p>An <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-absolute-with-fragment">absolute URL with fragment<a class="self-link" href="#syntax-url-absolute-with-fragment"></a></dfn> must be an <a data-link-type="dfn" href="#syntax-url-absolute">absolute URL</a>, optionally followed by "<code>#</code>" and a <a data-link-type="dfn" href="#syntax-url-fragment">fragment</a>. </p>
<p>An <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-absolute">absolute URL<a class="self-link" href="#syntax-url-absolute"></a></dfn> must be one of
the following </p>
<ul class="brief">
<li>
<p>a <a data-link-type="dfn" href="#syntax-url-scheme">scheme</a> that is an <a data-link-type="dfn" href="https://dom.spec.whatwg.org/#ascii-case-insensitive">ASCII case-insensitive</a> match for a <a data-link-type="dfn" href="#special-scheme">special scheme</a> and not an <a data-link-type="dfn" href="https://dom.spec.whatwg.org/#ascii-case-insensitive">ASCII case-insensitive</a> match
for "<code>file</code>", followed by "<code>:</code>" and a <a data-link-type="dfn" href="#syntax-url-scheme-relative">scheme-relative URL</a> </p>
<li>
<p>a <a data-link-type="dfn" href="#syntax-url-scheme">scheme</a> that is <em>not</em> an <a data-link-type="dfn" href="https://dom.spec.whatwg.org/#ascii-case-insensitive">ASCII case-insensitive</a> match for a <a data-link-type="dfn" href="#special-scheme">special scheme</a>, followed by
"<code>:</code>" and a <a data-link-type="dfn" href="#syntax-url-relative">relative URL</a> </p>
<li>
<p>a <a data-link-type="dfn" href="#syntax-url-scheme">scheme</a> that is an <a data-link-type="dfn" href="https://dom.spec.whatwg.org/#ascii-case-insensitive">ASCII case-insensitive</a> match for "<code>file</code>", followed by "<code>:</code>" and a <a data-link-type="dfn" href="#syntax-url-file-scheme-relative">scheme-relative file URL</a> </p>
</ul>
<p>any optionally followed by "<code>?</code>" and a <a data-link-type="dfn" href="#syntax-url-query">query</a>. </p>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-scheme">scheme<a class="self-link" href="#syntax-url-scheme"></a></dfn> must be one <a data-link-type="dfn" href="#ascii-alpha">ASCII alpha</a>, followed by zero or more of <a data-link-type="dfn" href="#ascii-alphanumeric">ASCII alphanumeric</a>,
"<code>+</code>", "<code>-</code>", and "<code>.</code>". <a data-link-type="dfn" href="#syntax-url-scheme">Schemes</a> should be registered in the <cite>IANA URI [sic] Schemes</cite> registry. <a data-link-type="biblio" href="#biblio-iana-uri-schemes">[IANA-URI-SCHEMES]</a> <a data-link-type="biblio" href="#biblio-rfc7595">[RFC7595]</a> </p>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-relative-with-fragment">relative URL with fragment<a class="self-link" href="#syntax-url-relative-with-fragment"></a></dfn> must be a <a data-link-type="dfn" href="#syntax-url-relative">relative URL</a>, optionally followed by "<code>#</code>" and a <a data-link-type="dfn" href="#syntax-url-fragment">fragment</a>. </p>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-relative">relative URL<a class="self-link" href="#syntax-url-relative"></a></dfn> must be one of
the following, switching on <a data-link-type="dfn" href="#concept-base-url">base URL</a>’s <a data-link-type="dfn" href="#concept-url-scheme">scheme</a>: </p>
<dl class="switch">
<dt>Not "<code>file</code>"
<dd>
<p>a <a data-link-type="dfn" href="#syntax-url-scheme-relative">scheme-relative URL</a> </p>
<dd>
<p>a <a data-link-type="dfn" href="#syntax-url-path-absolute">path-absolute URL</a> </p>
<dd>
<p>a <a data-link-type="dfn" href="#syntax-url-path-relative-scheme-less">path-relative scheme-less URL</a> </p>
<dt>"<code>file</code>"
<dd>
<p>a <a data-link-type="dfn" href="#syntax-url-file-scheme-relative">scheme-relative file URL</a> </p>
<dd>
<p>a <a data-link-type="dfn" href="#syntax-url-path-absolute">path-absolute URL</a> if <a data-link-type="dfn" href="#concept-base-url">base URL</a>’s <a data-link-type="dfn" href="#concept-url-host">host</a> is null </p>
<dd>
<p>a <a data-link-type="dfn" href="#syntax-url-file-path-absolute">path-absolute non-Windows-file URL</a> if <a data-link-type="dfn" href="#concept-base-url">base URL</a>’s <a data-link-type="dfn" href="#concept-url-host">host</a> is non-null </p>
<dd>
<p>a <a data-link-type="dfn" href="#syntax-url-path-relative-scheme-less">path-relative scheme-less URL</a> </p>
</dl>
<p>any optionally followed by "<code>?</code>" and a <a data-link-type="dfn" href="#syntax-url-query">query</a>. </p>
<p class="note no-backref" role="note">A non-null <a data-link-type="dfn" href="#concept-base-url">base URL</a> is necessary when <a data-link-type="dfn" href="#concept-url-parser">parsing</a> a <a data-link-type="dfn" href="#syntax-url-relative">relative URL</a>. </p>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-scheme-relative">scheme-relative URL<a class="self-link" href="#syntax-url-scheme-relative"></a></dfn> must be "<code>//</code>", followed by a <a data-link-type="dfn" href="#syntax-host">host</a>, optionally followed
by "<code>:</code>" and a <a data-link-type="dfn" href="#syntax-url-port">port</a>, optionally followed by a <a data-link-type="dfn" href="#syntax-url-path-absolute">path-absolute URL</a>. </p>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-port">port<a class="self-link" href="#syntax-url-port"></a></dfn> must be zero or more <a data-link-type="dfn" href="#ascii-digits">ASCII digits</a>. </p>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-file-scheme-relative">scheme-relative file URL<a class="self-link" href="#syntax-url-file-scheme-relative"></a></dfn> must be "<code>//</code>", followed by one of the following </p>
<ul class="brief">
<li>
<p>a <a data-link-type="dfn" href="#syntax-host">host</a>, optionally followed by a <a data-link-type="dfn" href="#syntax-url-file-path-absolute">path-absolute non-Windows-file URL</a> </p>
<li>
<p>a <a data-link-type="dfn" href="#syntax-url-path-absolute">path-absolute URL</a>. </p>
</ul>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-path-absolute">path-absolute URL<a class="self-link" href="#syntax-url-path-absolute"></a></dfn> must be
"<code>/</code>" followed by a <a data-link-type="dfn" href="#syntax-url-path-relative">path-relative URL</a>. </p>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-file-path-absolute">path-absolute non-Windows-file URL<a class="self-link" href="#syntax-url-file-path-absolute"></a></dfn> must be a <a data-link-type="dfn" href="#syntax-url-path-absolute">path-absolute URL</a> that does not start with "<code>/</code>", followed by
a <a data-link-type="dfn" href="#windows-drive-letter">Windows drive letter</a>, followed by "<code>/</code>". </p>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-path-relative">path-relative URL<a class="self-link" href="#syntax-url-path-relative"></a></dfn> must be
zero or more <a data-link-type="dfn" href="#syntax-url-path-segment">path segments</a>, separated from each other by "<code>/</code>", and not
start with "<code>/</code>". </p>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-path-relative-scheme-less">path-relative scheme-less URL<a class="self-link" href="#syntax-url-path-relative-scheme-less"></a></dfn> must be a <a data-link-type="dfn" href="#syntax-url-path-relative">path-relative URL</a> that does not start with a <a data-link-type="dfn" href="#syntax-url-scheme">scheme</a> and "<code>:</code>". </p>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-path-segment">path segment<a class="self-link" href="#syntax-url-path-segment"></a></dfn> must be one
of the following </p>
<ul class="brief">
<li>
<p>zero or more <a data-link-type="dfn" href="#url-units">URL units</a>, excluding "<code>/</code>" and "<code>?</code>",
that together are not a <a data-link-type="dfn" href="#syntax-url-path-segment-dot">single-dot path segment</a> or a <a data-link-type="dfn" href="#syntax-url-path-segment-dotdot">double-dot path segment</a>. </p>
<li>
<p>a <a data-link-type="dfn" href="#syntax-url-path-segment-dot">single-dot path segment</a> </p>
<li>
<p>a <a data-link-type="dfn" href="#syntax-url-path-segment-dotdot">double-dot path segment</a>. </p>
</ul>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-path-segment-dot">single-dot path segment<a class="self-link" href="#syntax-url-path-segment-dot"></a></dfn> must be "<code>.</code>" or an <a data-link-type="dfn" href="https://dom.spec.whatwg.org/#ascii-case-insensitive">ASCII case-insensitive</a> match for
"<code>%2e</code>". </p>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-path-segment-dotdot">double-dot path segment<a class="self-link" href="#syntax-url-path-segment-dotdot"></a></dfn> must be "<code>..</code>" or an <a data-link-type="dfn" href="https://dom.spec.whatwg.org/#ascii-case-insensitive">ASCII case-insensitive</a> match for
"<code>.%2e</code>", "<code>%2e.</code>", or "<code>%2e%2e</code>". </p>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-query">query<a class="self-link" href="#syntax-url-query"></a></dfn> must be zero or more <a data-link-type="dfn" href="#url-units">URL units</a>. </p>
<p>A <dfn data-dfn-for="urlsyntax" data-dfn-type="dfn" data-export="" id="syntax-url-fragment">fragment<a class="self-link" href="#syntax-url-fragment"></a></dfn> must be zero or more <a data-link-type="dfn" href="#url-units">URL units</a>. </p>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="url-code-points">URL code points<a class="self-link" href="#url-code-points"></a></dfn> are <a data-link-type="dfn" href="#ascii-alphanumeric">ASCII alphanumeric</a>,
"<code>!</code>",
"<code>$</code>",
"<code>&</code>",
"<code>'</code>",
"<code>(</code>",
"<code>)</code>",
"<code>*</code>",
"<code>+</code>",
"<code>,</code>",
"<code>-</code>",
"<code>.</code>",
"<code>/</code>",
"<code>:</code>",
"<code>;</code>",
"<code>=</code>",
"<code>?</code>",
"<code>@</code>",
"<code>_</code>",
"<code>~</code>",
and code points in the ranges
U+00A0 to U+D7FF,
U+E000 to
U+FDCF,
U+FDF0 to U+FFFD,
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+E0000 to U+EFFFD,
U+F0000 to U+FFFFD,
U+100000 to U+10FFFD. </p>
<p class="note" role="note">Code points higher than U+009F will be converted to <a data-link-type="dfn" href="#percent-encoded-byte">percent-encoded bytes</a> by the <a data-link-type="dfn" href="#concept-url-parser">URL parser</a>, except for code points appearing in <a data-link-type="dfn" href="#concept-url-fragment">fragments</a>. </p>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="url-units">URL units<a class="self-link" href="#url-units"></a></dfn> are <a data-link-type="dfn" href="#url-code-points">URL code points</a> and <a data-link-type="dfn" href="#percent-encoded-byte">percent-encoded bytes</a>. </p>
<p class="note" role="note"><a data-link-type="dfn" href="#percent-encoded-byte">Percent-encoded bytes</a> can be used to encode code points that are not <a data-link-type="dfn" href="#url-code-points">URL code points</a> or are excluded from a syntax production. </p>
<hr>
<p class="note no-backref" role="note">There is no conforming way to express a <a data-link-type="dfn" href="#concept-url-username">username</a> or <a data-link-type="dfn" href="#concept-url-password">password</a> of a <a data-link-type="dfn" href="#concept-url">URL record</a> within a <a data-link-type="dfn" href="#syntax-url">URL string</a>. </p>
<h3 class="heading settled" data-level="4.2" id="url-parsing"><span class="secno">4.2. </span><span class="content">URL parsing</span><a class="self-link" href="#url-parsing"></a></h3>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="concept-url-parser">URL parser<a class="self-link" href="#concept-url-parser"></a></dfn> takes a string <var>input</var>, with an optional <a data-link-type="dfn" href="#concept-base-url">base URL</a> <var>base</var> and an optional <a data-link-type="dfn" href="https://encoding.spec.whatwg.org/#encoding">encoding</a> <var>encoding override</var>, and then runs these steps: </p>
<p class="note no-backref" role="note">Non-web-browser implementations only need to implement the <a data-link-type="dfn" href="#concept-basic-url-parser">basic URL parser</a>. </p>
<ol>
<li>
<p>Let <var>url</var> be the result of running the <a data-link-type="dfn" href="#concept-basic-url-parser">basic URL parser</a> on <var>input</var> with <var>base</var>, and <var>encoding override</var> as provided. </p>
<li>
<p>If <var>url</var> is failure, return failure. </p>
<li>
<p>If <var>url</var>’s <a data-link-type="dfn" href="#concept-url-scheme">scheme</a> is not
"<code>blob</code>", return <var>url</var>. </p>
<li>
<p>If the first string in <var>url</var>’s <a data-link-type="dfn" href="#concept-url-path">path</a> is not in the <a data-link-type="dfn" href="https://w3c.github.io/FileAPI/#BlobURLStore">blob URL store</a>, return <var>url</var>. <a data-link-type="biblio" href="#biblio-fileapi">[FILEAPI]</a> </p>
<li>
<p>Set <var>url</var>’s <a data-link-type="dfn" href="#concept-url-object">object</a> to a <a data-link-type="dfn" href="https://html.spec.whatwg.org/multipage/infrastructure.html#structured-clone">StructuredClone</a> of the
entry in the <a data-link-type="dfn" href="https://w3c.github.io/FileAPI/#BlobURLStore">blob URL store</a> corresponding to the first string in <var>url</var>’s <a data-link-type="dfn" href="#concept-url-path">path</a>. <a data-link-type="biblio" href="#biblio-html">[HTML]</a> </p>
<li>
<p>Return <var>url</var>. </p>
</ol>
<hr>
<p>The <dfn data-dfn-type="dfn" data-noexport="" id="concept-basic-url-parser">basic URL parser<a class="self-link" href="#concept-basic-url-parser"></a></dfn> takes a string <var>input</var>, optionally with a <a data-link-type="dfn" href="#concept-base-url">base URL</a> <var>base</var>,
optionally with an <a data-link-type="dfn" href="https://encoding.spec.whatwg.org/#encoding">encoding</a> <var>encoding override</var>, optionally with an <a data-link-type="dfn" href="#concept-url">URL</a> <var>url</var> and a state override <var>state override</var>, and then runs these steps: </p>
<div class="note no-backref" role="note">
<p>The <var>encoding override</var> argument is a legacy concept only relevant for
HTML. The <var>url</var> and <var>state override</var> arguments are only for use by various APIs. <a data-link-type="biblio" href="#biblio-html">[HTML]</a> </p>
<p>When the <var>url</var> and <var>state override</var> arguments are not passed, the <a data-link-type="dfn" href="#concept-basic-url-parser">basic URL parser</a> returns either a new <a data-link-type="dfn" href="#concept-url">URL</a> or failure. If they are
passed, the algorithm simply modifies the passed <var>url</var> and can terminate without
returning anything. </p>
</div>
<ol>
<li>
<p>If <var>url</var> is not given: </p>
<ol>
<li>
<p>Set <var>url</var> to a new <a data-link-type="dfn" href="#concept-url">URL</a>. </p>
<li>
<p>If <var>input</var> contains any leading or trailing <a data-link-type="dfn" href="#c0-controls-and-space">C0 controls and space</a>, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>. </p>
<li>
<p>Remove any leading and trailing <a data-link-type="dfn" href="#c0-controls-and-space">C0 controls and space</a> from <var>input</var>. </p>
</ol>
<li>
<p>If <var>input</var> contains any <a data-link-type="dfn" href="#tab-and-newline">tab and newline</a>, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>. </p>
<li>
<p>Remove all <a data-link-type="dfn" href="#tab-and-newline">tab and newline</a> from <var>input</var>. </p>
<li>
<p>Let <var>state</var> be <var>state override</var> if given, or <a data-link-type="dfn" href="#scheme-start-state">scheme start state</a> otherwise. </p>
<li>
<p>If <var>base</var> is not given, set it to null. </p>
<li>
<p>Let <var>encoding</var> be <a data-link-type="dfn" href="https://encoding.spec.whatwg.org/#utf-8">UTF-8</a>. </p>
<li>
<p>If <var>encoding override</var> is given, set <var>encoding</var> to the result of <a data-link-type="dfn" href="https://encoding.spec.whatwg.org/#get-an-output-encoding">getting an output encoding</a> from <var>encoding override</var>. </p>
<li>
<p>Let <var>buffer</var> be the empty string. </p>
<li>
<p>Let the <var>@ flag</var> and the <var>[] flag</var> be
unset. </p>
<li>
<p>Let <var>pointer</var> be a pointer to first code point in <var>input</var>. </p>
<li>
<p>Keep running the following state machine by switching on <var>state</var>. If after a run <var>pointer</var> points to <a data-link-type="dfn" href="#eof-code-point">EOF code point</a>, go to the next step. Otherwise, increase <var>pointer</var> by one and continue with the state machine. </p>
<dl class="switch">
<dt><dfn data-dfn-type="dfn" data-noexport="" id="scheme-start-state">scheme start state<a class="self-link" href="#scheme-start-state"></a></dfn>
<dd>
<ol>
<li>
<p>If <a data-link-type="dfn" href="#c">c</a> is an <a data-link-type="dfn" href="#ascii-alpha">ASCII alpha</a>,
append <a data-link-type="dfn" href="#c">c</a>, <a data-link-type="dfn" href="#ascii-lowercase">lowercased</a>, to <var>buffer</var>, and
set <var>state</var> to <a data-link-type="dfn" href="#scheme-state">scheme state</a>. </p>
<li>
<p>Otherwise, if <var>state override</var> is not given, set <var>state</var> to <a data-link-type="dfn" href="#no-scheme-state">no scheme state</a>, and decrease <var>pointer</var> by one. </p>
<li>
<p>Otherwise, <a data-link-type="dfn" href="#syntax-violation">syntax violation</a>, terminate this algorithm. </p>
</ol>
<dt><dfn data-dfn-type="dfn" data-noexport="" id="scheme-state">scheme state<a class="self-link" href="#scheme-state"></a></dfn>
<dd>
<ol>
<li>
<p>If <a data-link-type="dfn" href="#c">c</a> is an <a data-link-type="dfn" href="#ascii-alphanumeric">ASCII alphanumeric</a>, "<code>+</code>",
"<code>-</code>", or "<code>.</code>", append <a data-link-type="dfn" href="#c">c</a>, <a data-link-type="dfn" href="#ascii-lowercase">lowercased</a>, to <var>buffer</var>. </p>
<li>
<p>Otherwise, if <a data-link-type="dfn" href="#c">c</a> is "<code>:</code>", run these substeps: </p>
<ol>
<li>
<p>If <var>state override</var> is given, run these subsubsteps: </p>
<ol>
<li>
<p>If <var>url</var>’s <a data-link-type="dfn" href="#concept-url-scheme">scheme</a> is a <a data-link-type="dfn" href="#special-scheme">special scheme</a> and <var>buffer</var> is not, terminate this algorithm. </p>
<li>
<p>If <var>url</var>’s <a data-link-type="dfn" href="#concept-url-scheme">scheme</a> is not a <a data-link-type="dfn" href="#special-scheme">special scheme</a> and <var>buffer</var> is, terminate this algorithm. </p>