urls.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html lang="en-US-x-Hixie" ><head><title>2.6 URLs — HTML5 </title><style type="text/css">
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fieldset p { margin: 0.5em 0; }
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position: fixed;
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display: block;
}
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}
.stability :link, .stability :visited,
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background: transparent;
color: white;
}
</style><link href="data:text/css,.impl%20%7B%20display:%20none;%20%7D%0Ahtml%20%7B%20border:%20solid%20yellow;%20%7D%20.domintro:before%20%7B%20display:%20none;%20%7D" id="author" rel="alternate stylesheet" title="Author documentation only"><link href="data:text/css,.impl%20%7B%20background:%20%23FFEEEE;%20%7D%20.domintro:before%20%7B%20background:%20%23FFEEEE;%20%7D" id="highlight" rel="alternate stylesheet" title="Highlight implementation
requirements"><link href="http://www.w3.org/StyleSheets/TR/W3C-WD" rel="stylesheet" type="text/css"><style type="text/css">
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#base64-table * { border: none; }
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white-space: nowrap;
font-size: 0.6em;
column-width: 30em;
column-gap: 1em;
-moz-column-width: 30em;
-moz-column-gap: 1em;
-webkit-column-width: 30em;
-webkit-column-gap: 1em;
}
#named-character-references-table > table > tbody > tr > td:first-child + td,
#named-character-references-table > table > tbody > tr > td:last-child { text-align: center; }
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font-family: 'Essays1743';
src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743.ttf');
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font-family: 'Essays1743';
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src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743-Bold.ttf');
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src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743-BoldItalic.ttf');
}
</style><style type="text/css">
.domintro:before { display: table; margin: -1em -0.5em -0.5em auto; width: auto; content: 'This box is non-normative. Implementation requirements are given below this box.'; color: black; font-style: italic; border: solid 2px; background: white; padding: 0 0.25em; }
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<p class="stability" id="wip"><strong>This is a work in
progress!</strong> For the latest updates from the HTML WG, possibly
including important bug fixes, please look at the <a href="http://dev.w3.org/html5/spec/Overview.html">editor's draft</a> instead.
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<a href="http://www.w3.org/TR/html5">up-to-date Working Draft</a>
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<h1>HTML5</h1>
</div><div>
<a href="common-microsyntaxes.html" class="prev">2.5 Common microsyntaxes</a> –
<a href="spec.html#contents">Table of contents</a> –
<a href="fetching-resources.html" class="next">2.7 Fetching resources</a>
<ol class="toc"><li><ol><li><a href="urls.html#urls"><span class="secno">2.6 </span>URLs</a>
<ol><li><a href="urls.html#terminology-0"><span class="secno">2.6.1 </span>Terminology</a></li><li><a href="urls.html#parsing-urls"><span class="secno">2.6.2 </span>Parsing URLs</a></li><li><a href="urls.html#resolving-urls"><span class="secno">2.6.3 </span>Resolving URLs</a></li><li><a href="urls.html#url-manipulation-and-creation"><span class="secno">2.6.4 </span>URL manipulation and creation</a></li><li><a href="urls.html#dynamic-changes-to-base-urls"><span class="secno">2.6.5 </span>Dynamic changes to base URLs</a></li><li><a href="urls.html#interfaces-for-url-manipulation"><span class="secno">2.6.6 </span>Interfaces for URL manipulation</a></li></ol></li></ol></li></ol></div>
<h3 id="urls"><span class="secno">2.6 </span>URLs</h3><p>This specification defines the term <a href="#url">URL</a>, and defines
various algorithms for dealing with URLs, because for historical
reasons the rules defined by the URI and IRI specifications are not
a complete description of what HTML user agents need to implement to
be compatible with Web content.</p><p class="note">The term "URL" in this specification is used in a
manner distinct from the precise technical meaning it is given in
RFC 3986. Readers familiar with that RFC will find it easier to read
<em>this</em> specification if they pretend the term "URL" as used
herein is really called something else altogether. This is a
<a href="introduction.html#willful-violation">willful violation</a> of RFC 3986. <a href="references.html#refsRFC3986">[RFC3986]</a></p><h4 id="terminology-0"><span class="secno">2.6.1 </span>Terminology</h4><p>A <dfn id="url">URL</dfn> is a string used to identify a resource.</p><p>A <a href="#url">URL</a> is a <dfn id="valid-url">valid URL</dfn> if at least one of
the following conditions holds:</p><ul><li><p>The <a href="#url">URL</a> is a valid URI reference <a href="references.html#refsRFC3986">[RFC3986]</a>.</p></li>
<li><p>The <a href="#url">URL</a> is a valid IRI reference and it has no
query component. <a href="references.html#refsRFC3987">[RFC3987]</a></p></li>
<li><p>The <a href="#url">URL</a> is a valid IRI reference and its query
component contains no unescaped non-ASCII characters. <a href="references.html#refsRFC3987">[RFC3987]</a></p></li>
<li><p>The <a href="#url">URL</a> is a valid IRI reference and the <a href="dom.html#document-s-character-encoding" title="document's character encoding">character encoding</a> of
the URL's <code><a href="infrastructure.html#document">Document</a></code> is UTF-8 or UTF-16. <a href="references.html#refsRFC3987">[RFC3987]</a></p></li>
</ul><p>A string is a <dfn id="valid-non-empty-url">valid non-empty URL</dfn> if it is a
<a href="#valid-url">valid URL</a> but it is not the empty string.</p><p>A string is a <dfn id="valid-url-potentially-surrounded-by-spaces">valid URL potentially surrounded by
spaces</dfn> if, after <a href="common-microsyntaxes.html#strip-leading-and-trailing-whitespace" title="strip leading and trailing
whitespace">stripping leading and trailing whitespace</a> from
it, it is a <a href="#valid-url">valid URL</a>.</p><p>A string is a <dfn id="valid-non-empty-url-potentially-surrounded-by-spaces">valid non-empty URL potentially surrounded by
spaces</dfn> if, after <a href="common-microsyntaxes.html#strip-leading-and-trailing-whitespace" title="strip leading and trailing
whitespace">stripping leading and trailing whitespace</a> from
it, it is a <a href="#valid-non-empty-url">valid non-empty URL</a>.</p><p>This specification defines the URL
<dfn id="about:legacy-compat"><code>about:legacy-compat</code></dfn> as a reserved, though
unresolvable, <code title="">about:</code> URI, for use in <a href="syntax.html#syntax-doctype" title="syntax-doctype">DOCTYPE</a>s in <a href="dom.html#html-documents">HTML
documents</a> when needed for compatibility with XML tools. <a href="references.html#refsABOUT">[ABOUT]</a></p><p>This specification defines the URL
<dfn id="about:srcdoc"><code>about:srcdoc</code></dfn> as a reserved, though
unresolvable, <code title="">about:</code> URI, that is used as
<a href="dom.html#the-document-s-address">the document's address</a> of <a href="the-iframe-element.html#an-iframe-srcdoc-document" title="an iframe srcdoc
document"><code>iframe</code> <code title="attr-iframe-srcdoc">srcdoc</code> documents</a>. <a href="references.html#refsABOUT">[ABOUT]</a></p><div class="impl">
<h4 id="parsing-urls"><span class="secno">2.6.2 </span>Parsing URLs</h4>
<p>To <dfn id="parse-a-url">parse a URL</dfn> <var title="">url</var> into its
component parts, the user agent must use the following steps:</p>
<ol><li><p>Strip leading and trailing <a href="common-microsyntaxes.html#space-character" title="space
character">space characters</a> from <var title="">url</var>.</p></li>
<li>
<p>Parse <var title="">url</var> in the manner defined by RFC
3986, with the following exceptions:</p>
<ul><li>Add all characters with code points less than or equal to
U+0020 or greater than or equal to U+007F to the
<unreserved> production.</li>
<li>Add the characters U+0022, U+003C, U+003E, U+005B .. U+005E,
U+0060, and U+007B .. U+007D to the <unreserved>
production.
<!--
0022 QUOTATION MARK
003C LESS-THAN SIGN
003E GREATER-THAN SIGN
005B LEFT SQUARE BRACKET
005C REVERSE SOLIDUS
005D RIGHT SQUARE BRACKET
005E CIRCUMFLEX ACCENT
0060 GRAVE ACCENT
007B LEFT CURLY BRACKET
007C VERTICAL LINE
007D RIGHT CURLY BRACKET
-->
</li>
<li>Add a single U+0025 PERCENT SIGN character as a second
alternative way of matching the <pct-encoded> production,
except when the <pct-encoded> is used in the
<reg-name> production.</li>
<li>Add the U+0023 NUMBER SIGN character to the characters
allowed in the <fragment> production.</li>
</ul></li>
<li>
<p>If <var title="">url</var> doesn't match the
<URI-reference> production, even after the above changes are
made to the ABNF definitions, then parsing the URL fails with an
error. <a href="references.html#refsRFC3986">[RFC3986]</a></p>
<p>Otherwise, parsing <var title="">url</var> was successful; the
components of the URL are substrings of <var title="">url</var>
defined as follows:</p>
<dl><dt><dfn id="url-scheme" title="url-scheme"><scheme></dfn></dt>
<dd><p>The substring matched by the <scheme> production, if any.</p></dd>
<dt><dfn id="url-host" title="url-host"><host></dfn></dt>
<dd><p>The substring matched by the <host> production, if any.</p></dd>
<dt><dfn id="url-port" title="url-port"><port></dfn></dt>
<dd><p>The substring matched by the <port> production, if any.</p></dd>
<dt><dfn id="url-hostport" title="url-hostport"><hostport></dfn></dt>
<dd><p>If there is a <scheme> component and a <port>
component and the port given by the <port> component is
different than the default port defined for the protocol given by
the <scheme> component, then <hostport> is the
substring that starts with the substring matched by the
<host> production and ends with the substring matched by the
<port> production, and includes the colon in between the
two. Otherwise, it is the same as the <host> component.</p>
</dd><dt><dfn id="url-path" title="url-path"><path></dfn></dt>
<dd>
<p>The substring matched by one of the following productions, if
one of them was matched:</p>
<ul class="brief"><li><path-abempty></li>
<li><path-absolute></li>
<li><path-noscheme></li>
<li><path-rootless></li>
<li><path-empty></li>
</ul></dd>
<dt><dfn id="url-query" title="url-query"><query></dfn></dt>
<dd><p>The substring matched by the <query> production, if any.</p></dd>
<dt><dfn id="url-fragment" title="url-fragment"><fragment></dfn></dt>
<dd><p>The substring matched by the <fragment> production, if any.</p></dd>
<dt><dfn id="url-host-specific" title="url-host-specific"><host-specific></dfn></dt>
<dd><p>The substring that <em>follows</em> the substring matched
by the <authority> production, or the whole string if the
<authority> production wasn't matched.</p></dd>
</dl></li>
</ol><p class="note">These parsing rules are a <a href="introduction.html#willful-violation">willful
violation</a> of RFC 3986 and RFC 3987 (which do not define error
handling), motivated by a desire to handle legacy content. <a href="references.html#refsRFC3986">[RFC3986]</a> <a href="references.html#refsRFC3987">[RFC3987]</a></p>
</div><h4 id="resolving-urls"><span class="secno">2.6.3 </span>Resolving URLs</h4><p>Resolving a URL is the process of taking a relative URL and
obtaining the absolute URL that it implies.</p><div class="impl">
<p>To <dfn id="resolve-a-url">resolve a URL</dfn> to an <a href="#absolute-url">absolute URL</a>
relative to either another <a href="#absolute-url">absolute URL</a> or an element,
the user agent must use the following steps. Resolving a URL can
result in an error, in which case the URL is not resolvable.</p>
<ol><li><p>Let <var title="">url</var> be the <a href="#url">URL</a> being
resolved.</p></li>
<li>
<p>Let <var title="">encoding</var> be determined as follows:</p>
<dl class="switch"><dt>If the URL had a character encoding defined when the URL was
created or defined</dt>
<dd>The URL character encoding is as defined.</dd>
<dt>If the URL came from a script (e.g. as an argument to a
method)</dt>
<dd>The URL character encoding is the <a href="webappapis.html#script-s-url-character-encoding">script's URL character
encoding</a>.</dd>
<dt>If the URL came from a DOM node (e.g. from an element)</dt>
<dd>The node has a <code><a href="infrastructure.html#document">Document</a></code>, and the URL character
encoding is the <a href="dom.html#document-s-character-encoding">document's character encoding</a>.</dd>
</dl></li>
<li><p>If <var title="">encoding</var> is a UTF-16 encoding, then
change the value of <var title="">encoding</var> to UTF-8.</p></li>
<li>
<p>If the algorithm was invoked with an <a href="#absolute-url">absolute URL</a>
to use as the base URL, let <var title="">base</var> be that
<a href="#absolute-url">absolute URL</a>.</p>
<p>Otherwise, let <var title="">base</var> be the <i>base URI of
the element</i>, as defined by the XML Base specification, with
<i>the base URI of the document entity</i> being defined as the
<a href="#document-base-url">document base URL</a> of the <code><a href="infrastructure.html#document">Document</a></code> that
owns the element. <a href="references.html#refsXMLBASE">[XMLBASE]</a></p>
<p>For the purposes of the XML Base specification, user agents
must act as if all <code><a href="infrastructure.html#document">Document</a></code> objects represented XML
documents.</p>
<p class="note">It is possible for <code title="attr-xml-base"><a href="elements.html#the-xml:base-attribute-xml-only">xml:base</a></code> attributes to be present
even in HTML fragments, as such attributes can be added
dynamically using script. (Such scripts would not be conforming,
however, as <code title="attr-xml-base"><a href="elements.html#the-xml:base-attribute-xml-only">xml:base</a></code> attributes
are not allowed in <a href="dom.html#html-documents">HTML documents</a>.)</p>
<p>The <dfn id="document-base-url">document base URL</dfn> of a <code><a href="infrastructure.html#document">Document</a></code>
object is the <a href="#absolute-url">absolute URL</a> obtained by running these
substeps:</p>
<ol><li><p>Let <var title="">fallback base url</var> be <a href="dom.html#the-document-s-address">the
document's address</a>.</p></li>
<li>
<p>If <var title="">fallback base url</var> is
<code><a href="fetching-resources.html#about:blank">about:blank</a></code>, and the <code><a href="infrastructure.html#document">Document</a></code>'s
<a href="browsers.html#browsing-context">browsing context</a> has a <a href="browsers.html#creator-browsing-context">creator browsing
context</a>, then let <var title="">fallback base url</var>
be the <a href="#document-base-url">document base URL</a> of the <a href="browsers.html#creator-document">creator
<code>Document</code></a> instead.</p>
</li>
<li><p>If the <code><a href="infrastructure.html#document">Document</a></code> is <a href="the-iframe-element.html#an-iframe-srcdoc-document">an
<code>iframe</code> <code title="attr-iframe-srcdoc">srcdoc</code> document</a>, then
let <var title="">fallback base url</var> be the <a href="#document-base-url">document
base URL</a> of the <code><a href="infrastructure.html#document">Document</a></code>'s <a href="browsers.html#browsing-context">browsing
context</a>'s <a href="browsers.html#browsing-context-container">browsing context container</a>'s
<code><a href="infrastructure.html#document">Document</a></code> instead.</p></li>
<li><p>If there is no <code><a href="semantics.html#the-base-element">base</a></code> element that has an <code title="attr-base-href"><a href="semantics.html#attr-base-href">href</a></code> attribute, then the
<a href="#document-base-url">document base URL</a> is <var title="">fallback base
url</var>; abort these steps. Otherwise, let <var title="">url</var> be the value of the <code title="attr-base-href"><a href="semantics.html#attr-base-href">href</a></code> attribute of the first such
element.</p></li>
<li><p><a href="#resolve-a-url" title="resolve a URL">Resolve</a> <var title="">url</var> relative to <var title="">fallback base
url</var> (thus, the <code><a href="semantics.html#the-base-element">base</a></code> <code title="attr-base-href"><a href="semantics.html#attr-base-href">href</a></code> attribute isn't affected by
<code title="attr-xml-base"><a href="elements.html#the-xml:base-attribute-xml-only">xml:base</a></code> attributes).</p></li>
<li><p>The <a href="#document-base-url">document base URL</a> is the result of the
previous step if it was successful; otherwise it is <var title="">fallback base url</var>.</p></li>
</ol></li>
<li><p><a href="#parse-a-url" title="parse a URL">Parse</a> <var title="">url</var> into its component parts.</p></li>
<li>
<p>If parsing <var title="">url</var> resulted in a <a href="#url-host" title="url-host"><host></a> component, then replace the
matching substring of <var title="">url</var> with the string that
results from expanding any sequences of percent-encoded octets in
that component that are valid UTF-8 sequences into Unicode
characters as defined by UTF-8.</p>
<p>If any percent-encoded octets in that component are not valid
UTF-8 sequences, then return an error and abort these steps.</p>
<p>Apply the IDNA ToASCII algorithm to the matching substring,
with both the AllowUnassigned and UseSTD3ASCIIRules flags
set. Replace the matching substring with the result of the ToASCII
algorithm.</p>
<p>If ToASCII fails to convert one of the components of the
string, e.g. because it is too long or because it contains invalid
characters, then return an error and abort these steps. <a href="references.html#refsRFC3490">[RFC3490]</a></p>
</li>
<li>
<p>If parsing <var title="">url</var> resulted in a <a href="#url-path" title="url-path"><path></a> component, then replace the
matching substring of <var title="">url</var> with the string that
results from applying the following steps to each character other
than U+0025 PERCENT SIGN (%) that doesn't match the original
<path> production defined in RFC 3986:</p>
<ol><li>Encode the character into a sequence of octets as defined by
UTF-8.</li>
<li>Replace the character with the percent-encoded form of those
octets. <a href="references.html#refsRFC3986">[RFC3986]</a></li>
</ol><div class="example">
<p>For instance if <var title="">url</var> was "<code title="">//example.com/a^b☺c%FFd%z/?e</code>", then the
<a href="#url-path" title="url-path"><path></a> component's substring
would be "<code title="">/a^b☺c%FFd%z/</code>" and the two
characters that would have to be escaped would be "<code title="">^</code>" and "<code title="">☺</code>". The
result after this step was applied would therefore be that <var title="">url</var> now had the value "<code title="">//example.com/a%5Eb%E2%98%BAc%FFd%z/?e</code>".</p>
</div>
</li>
<li>
<p>If parsing <var title="">url</var> resulted in a <a href="#url-query" title="url-query"><query></a> component, then replace the
matching substring of <var title="">url</var> with the string that
results from applying the following steps to each character other
than U+0025 PERCENT SIGN (%) that doesn't match the original
<query> production defined in RFC 3986:</p>
<ol><li>If the character in question cannot be expressed in the
encoding <var title="">encoding</var>, then replace it with a
single 0x3F octet (an ASCII question mark) and skip the remaining
substeps for this character.</li>
<li>Encode the character into a sequence of octets as defined by
the encoding <var title="">encoding</var>.</li>
<li>Replace the character with the percent-encoded form of those
octets. <a href="references.html#refsRFC3986">[RFC3986]</a></li>
</ol></li>
<li><p>Apply the algorithm described in RFC 3986 section 5.2
Relative Resolution, using <var title="">url</var> as the
potentially relative URI reference (<var title="">R</var>), and
<var title="">base</var> as the base URI (<var title="">Base</var>). <a href="references.html#refsRFC3986">[RFC3986]</a></p></li>
<li>
<p>Apply any relevant conformance criteria of RFC 3986 and RFC
3987, returning an error and aborting these steps if
appropriate. <a href="references.html#refsRFC3986">[RFC3986]</a> <a href="references.html#refsRFC3987">[RFC3987]</a></p>
<p class="example">For instance, if an absolute URI that would be
returned by the above algorithm violates the restrictions specific
to its scheme, e.g. a <code title="">data:</code> URI using the
"<code title="">//</code>" server-based naming authority syntax,
then user agents are to treat this as an error instead.</p>
</li>
<li><p>Let <var title="">result</var> be the target URI (<var title="">T</var>) returned by the Relative Resolution
algorithm.</p></li>
<li><p>If <var title="">result</var> uses a scheme with a
server-based naming authority, replace all U+005C REVERSE SOLIDUS
(\) characters in <var title="">result</var> with U+002F SOLIDUS
(/) characters.</p></li>
<li><p>Return <var title="">result</var>.</p></li>
</ol><p class="note">Some of the steps in these rules, for example the
processing of U+005C REVERSE SOLIDUS (\) characters, are a
<a href="introduction.html#willful-violation">willful violation</a> of RFC 3986 and RFC 3987, motivated
by a desire to handle legacy content. <a href="references.html#refsRFC3986">[RFC3986]</a> <a href="references.html#refsRFC3987">[RFC3987]</a></p>
</div><p>A <a href="#url">URL</a> is an <dfn id="absolute-url">absolute URL</dfn> if <a href="#resolve-a-url" title="resolve a url">resolving</a> it results in the same output
regardless of what it is resolved relative to, and that output is
not a failure.</p><p>An <a href="#absolute-url">absolute URL</a> is a <dfn id="hierarchical-url">hierarchical URL</dfn> if,
when <a href="#resolve-a-url" title="resolve a url">resolved</a> and then <a href="#parse-a-url" title="parse a url">parsed</a>, there is a character immediately
after the <a href="#url-scheme" title="url-scheme"><scheme></a> component
and it is a U+002F SOLIDUS character (/).</p><p>An <a href="#absolute-url">absolute URL</a> is an <dfn id="authority-based-url">authority-based URL</dfn>
if, when <a href="#resolve-a-url" title="resolve a url">resolved</a> and then <a href="#parse-a-url" title="parse a url">parsed</a>, there are two characters
immediately after the <a href="#url-scheme" title="url-scheme"><scheme></a>
component and they are both U+002F SOLIDUS characters (//).</p><div class="impl">
<h4 id="url-manipulation-and-creation"><span class="secno">2.6.4 </span>URL manipulation and creation</h4>
<p>To <dfn id="fragment-escaped" title="fragment-escaped">fragment-escape</dfn> a string
<var title="">input</var>, a user agent must run the following
steps:</p>
<ol><li><p>Let <var title="">input</var> be the string to be
escaped.</p></li>
<li><p>Let <var title="">position</var> point at the first
character of <var title="">input</var>.</p></li>
<li><p>Let <var title="">output</var> be an empty string.</p></li>
<li><p><i>Loop</i>: If <var title="">position</var> is past the end
of <var title="">input</var>, then jump to the step labeled
<i>end</i>.</p></li>
<li>
<p>If the character in <var title="">input</var> pointed to by
<var title="">position</var> is in the range U+0000 to U+0020 or
is one of the following characters:</p>
<ul class="brief"><li>U+0022 QUOTATION MARK character (")
</li><li>U+0023 NUMBER SIGN character (#)
</li><li>U+0025 PERCENT SIGN character (%)
</li><li>U+003C LESS-THAN SIGN character (<)
</li><li>U+003E GREATER-THAN SIGN character (>)
</li><li>U+005B LEFT SQUARE BRACKET character ([)
</li><li>U+005C REVERSE SOLIDUS character (\)
</li><li>U+005D RIGHT SQUARE BRACKET character (])
</li><li>U+005E CIRCUMFLEX ACCENT character (^)
</li><li>U+007B LEFT CURLY BRACKET character ({)
</li><li>U+007C VERTICAL LINE character (|)
</li><li>U+007D RIGHT CURLY BRACKET character (})
</li></ul><p>...then append the percent-encoded form of the character to
<var title="">output</var>. <a href="references.html#refsRFC3986">[RFC3986]</a></p>
<p>Otherwise, append the character itself to <var title="">output</var>.</p>
<p class="note">This escapes any ASCII characters that are not
valid in the URI <fragment> production without being
escaped.</p>
</li>
<li><p>Advance <var title="">position</var> to the next character
in <var title="">input</var>.</p></li>
<li><p>Return to the step labeled <i>loop</i>.</p></li>
<li><p><i>End</i>: Return <var title="">output</var>.</p></li>
</ol></div><div class="impl">
<h4 id="dynamic-changes-to-base-urls"><span class="secno">2.6.5 </span>Dynamic changes to base URLs</h4>
<p>When an <code title="attr-xml-base"><a href="elements.html#the-xml:base-attribute-xml-only">xml:base</a></code> attribute
changes, the attribute's element, and all descendant elements, are
<a href="#affected-by-a-base-url-change">affected by a base URL change</a>.</p>
<p>When a document's <a href="#document-base-url">document base URL</a> changes, all
elements in that document are <a href="#affected-by-a-base-url-change">affected by a base URL
change</a>.</p>
<p>When an element is moved from one document to another, if the two
documents have different <a href="#document-base-url" title="document base URL">base
URLs</a>, then that element and all its descendants are
<a href="#affected-by-a-base-url-change">affected by a base URL change</a>.</p>
<p>When an element is <dfn id="affected-by-a-base-url-change">affected by a base URL change</dfn>, it
must act as described in the following list:</p>
<dl class="switch"><dt>If the element creates a <a href="links.html#hyperlink">hyperlink</a></dt>
<dd>
<p>If the <a href="#absolute-url">absolute URL</a> identified by the hyperlink is
being shown to the user, or if any data derived from that URL is
affecting the display, then the <code title="attr-hyperlink-href"><a href="links.html#attr-hyperlink-href">href</a></code> attribute should be <a href="#resolve-a-url" title="resolve a url">re-resolved</a> relative to the element
and the UI updated appropriately.</p>
<p class="example">For example, the CSS <code title="selector-link"><a href="links.html#selector-link">:link</a></code>/<code title="selector-visited"><a href="links.html#selector-visited">:visited</a></code> pseudo-classes might have
been affected.</p>
</dd>
<dt>If the element is a <code><a href="text-level-semantics.html#the-q-element">q</a></code>, <code><a href="grouping-content.html#the-blockquote-element">blockquote</a></code>,
<code><a href="sections.html#the-section-element">section</a></code>, <code><a href="sections.html#the-article-element">article</a></code>, <code><a href="edits.html#the-ins-element">ins</a></code>, or
<code><a href="edits.html#the-del-element">del</a></code> element with a <code title="">cite</code>
attribute</dt>
<dd>
<p>If the <a href="#absolute-url">absolute URL</a> identified by the <code title="">cite</code> attribute is being shown to the user, or if
any data derived from that URL is affecting the display, then the
<a href="#url">URL</a> should be <a href="#resolve-a-url" title="resolve a
url">re-resolved</a> relative to the element and the UI updated
appropriately.</p>
</dd>
<dt>Otherwise</dt>
<dd>
<p>The element is not directly affected.</p>
<p class="example">Changing the base URL doesn't affect the image
displayed by <code><a href="embedded-content-1.html#the-img-element">img</a></code> elements, although subsequent
accesses of the <code title="dom-img-src"><a href="embedded-content-1.html#dom-img-src">src</a></code> IDL attribute
from script will return a new <a href="#absolute-url">absolute URL</a> that might
no longer correspond to the image being shown.</p>
</dd>
</dl></div><h4 id="interfaces-for-url-manipulation"><span class="secno">2.6.6 </span>Interfaces for URL manipulation</h4><p>An interface that has a complement of <dfn id="url-decomposition-idl-attributes">URL decomposition IDL
attributes</dfn> has seven attributes with the following
definitions:</p><pre class="idl extract"> attribute DOMString <a href="#dom-uda-protocol" title="dom-uda-protocol">protocol</a>;
attribute DOMString <a href="#dom-uda-host" title="dom-uda-host">host</a>;
attribute DOMString <a href="#dom-uda-hostname" title="dom-uda-hostname">hostname</a>;
attribute DOMString <a href="#dom-uda-port" title="dom-uda-port">port</a>;
attribute DOMString <a href="#dom-uda-pathname" title="dom-uda-pathname">pathname</a>;
attribute DOMString <a href="#dom-uda-search" title="dom-uda-search">search</a>;
attribute DOMString <a href="#dom-uda-hash" title="dom-uda-hash">hash</a>;</pre><dl class="domintro"><dt><var title="">o</var> . <code title="dom-uda-protocol"><a href="#dom-uda-protocol">protocol</a></code> [ = <var title="">value</var> ]</dt>
<dd>
<p>Returns the current scheme of the underlying URL.</p>
<p>Can be set, to change the underlying URL's scheme.</p>
</dd>
<dt><var title="">o</var> . <code title="dom-uda-host"><a href="#dom-uda-host">host</a></code> [ = <var title="">value</var> ]</dt>
<dd>
<p>Returns the current host and port (if it's not the default port) in the underlying URL.</p>
<p>Can be set, to change the underlying URL's host and port.</p>
<p>The host and the port are separated by a colon. The port part,
if omitted, will be assumed to be the current scheme's default
port.</p>
</dd>
<dt><var title="">o</var> . <code title="dom-uda-hostname"><a href="#dom-uda-hostname">hostname</a></code> [ = <var title="">value</var> ]</dt>
<dd>
<p>Returns the current host in the underlying URL.</p>
<p>Can be set, to change the underlying URL's host.</p>
</dd>
<dt><var title="">o</var> . <code title="dom-uda-port"><a href="#dom-uda-port">port</a></code> [ = <var title="">value</var> ]</dt>
<dd>
<p>Returns the current port in the underlying URL.</p>
<p>Can be set, to change the underlying URL's port.</p>
</dd>
<dt><var title="">o</var> . <code title="dom-uda-pathname"><a href="#dom-uda-pathname">pathname</a></code> [ = <var title="">value</var> ]</dt>
<dd>
<p>Returns the current path in the underlying URL.</p>
<p>Can be set, to change the underlying URL's path.</p>
</dd>
<dt><var title="">o</var> . <code title="dom-uda-search"><a href="#dom-uda-search">search</a></code> [ = <var title="">value</var> ]</dt>
<dd>
<p>Returns the current query component in the underlying URL.</p>
<p>Can be set, to change the underlying URL's query component.</p>
</dd>
<dt><var title="">o</var> . <code title="dom-uda-hash"><a href="#dom-uda-hash">hash</a></code> [ = <var title="">value</var> ]</dt>
<dd>
<p>Returns the current fragment identifier in the underlying URL.</p>
<p>Can be set, to change the underlying URL's fragment identifier.</p>
</dd>
</dl><div class="impl">
<hr><p>The attributes defined to be <a href="#url-decomposition-idl-attributes">URL decomposition IDL
attributes</a> must act as described for the attributes with the
same corresponding names in this section.</p>
<p>In addition, an interface with a complement of <a href="#url-decomposition-idl-attributes">URL
decomposition IDL attributes</a> defines an <dfn id="concept-uda-input" title="concept-uda-input">input</dfn>, which is a <a href="#url">URL</a>
that the attributes act on, and a <dfn id="concept-uda-setter" title="concept-uda-setter">common setter action</dfn>, which is a
set of steps invoked when any of the attributes' setters are
invoked.</p>
<p>The seven <a href="#url-decomposition-idl-attributes">URL decomposition IDL attributes</a> have
similar requirements.</p>
<p>On getting, if the <a href="#concept-uda-input" title="concept-uda-input">input</a>
is an <a href="#absolute-url">absolute URL</a> that fulfills the condition given in
the "getter condition" column corresponding to the attribute in the
table below, the user agent must return the part of the <a href="#concept-uda-input" title="concept-uda-input">input</a> URL given in the "component"
column, with any prefixes specified in the "prefix" column
appropriately added to the start of the string and any suffixes
specified in the "suffix" column appropriately added to the end of
the string. Otherwise, the attribute must return the empty
string.</p>
<p>On setting, the new value must first be mutated as described by
the "setter preprocessor" column, then mutated by %-escaping any
characters in the new value that are not valid in the relevant
component as given by the "component" column. Then, if the <a href="#concept-uda-input" title="concept-uda-input">input</a> is an <a href="#absolute-url">absolute
URL</a> and the resulting new value fulfills the condition given
in the "setter condition" column, the user agent must make a new
string <var title="">output</var> by replacing the component of the
URL given by the "component" column in the <a href="#concept-uda-input" title="concept-uda-input">input</a> URL with the new value;
otherwise, the user agent must let <var title="">output</var> be
equal to the <a href="#concept-uda-input" title="concept-uda-input">input</a>. Finally,
the user agent must invoke the <a href="#concept-uda-setter" title="concept-uda-setter">common setter action</a> with the
value of <var title="">output</var>.</p>
<p>When replacing a component in the URL, if the component is part
of an optional group in the URL syntax consisting of a character
followed by the component, the component (including its prefix
character) must be included even if the new value is the empty
string.</p>
<p class="note">The previous paragraph applies in particular to the
"<code title="">:</code>" before a <port> component, the "<code title="">?</code>" before a <query> component, and the "<code title="">#</code>" before a <fragment> component.</p>
<p>For the purposes of the above definitions, URLs must be parsed
using the <a href="#parse-a-url" title="parse a URL">URL parsing rules</a> defined
in this specification.</p>
<table id="table-uda"><thead><tr><th>Attribute
</th><th>Component
</th><th>Getter Condition
</th><th>Prefix
</th><th>Suffix
</th><th>Setter Preprocessor
</th><th>Setter Condition
</th></tr></thead><tbody><tr><td><dfn id="dom-uda-protocol" title="dom-uda-protocol"><code>protocol</code></dfn>
</td><td><a href="#url-scheme" title="url-scheme"><scheme></a>
</td><td>—
</td><td>—
</td><td>U+003A COLON (:)
</td><td>Remove all trailing U+003A COLON characters (:)
</td><td>The new value is not the empty string
</td></tr><tr><td><dfn id="dom-uda-host" title="dom-uda-host"><code>host</code></dfn>
</td><td><a href="#url-hostport" title="url-hostport"><hostport></a>
</td><td><a href="#concept-uda-input" title="concept-uda-input">input</a> is an <a href="#authority-based-url">authority-based URL</a>
</td><td>—
</td><td>—
</td><td>—
</td><td>The new value is not the empty string and <a href="#concept-uda-input" title="concept-uda-input">input</a> is an <a href="#authority-based-url">authority-based URL</a>
</td></tr><tr><td><dfn id="dom-uda-hostname" title="dom-uda-hostname"><code>hostname</code></dfn>
</td><td><a href="#url-host" title="url-host"><host></a>
</td><td><a href="#concept-uda-input" title="concept-uda-input">input</a> is an <a href="#authority-based-url">authority-based URL</a>
</td><td>—
</td><td>—
</td><td>Remove all leading U+002F SOLIDUS characters (/)
</td><td>The new value is not the empty string and <a href="#concept-uda-input" title="concept-uda-input">input</a> is an <a href="#authority-based-url">authority-based URL</a>
</td></tr><tr><td><dfn id="dom-uda-port" title="dom-uda-port"><code>port</code></dfn>
</td><td><a href="#url-port" title="url-port"><port></a>
</td><td><a href="#concept-uda-input" title="concept-uda-input">input</a> is an <a href="#authority-based-url">authority-based URL</a>, and contained a <a href="#url-port" title="url-port"><port></a> component (possibly an empty one)
</td><td>—
</td><td>—
</td><td>Remove all characters in the new value from the first that is not in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), if any.
Remove any leading U+0030 DIGIT ZERO characters (0) in the new value.
If the resulting string is empty, set it to a single U+0030 DIGIT ZERO character (0).
</td><td><a href="#concept-uda-input" title="concept-uda-input">input</a> is an <a href="#authority-based-url">authority-based URL</a>,
and the new value, when interpreted as a base-ten integer, is less than or equal to 65535
</td></tr><tr><td><dfn id="dom-uda-pathname" title="dom-uda-pathname"><code>pathname</code></dfn>
</td><td><a href="#url-path" title="url-path"><path></a>
</td><td><a href="#concept-uda-input" title="concept-uda-input">input</a> is a <a href="#hierarchical-url">hierarchical URL</a>
</td><td>—
</td><td>—
</td><td>If it has no leading U+002F SOLIDUS character (/), prepend a U+002F SOLIDUS character (/) to the new value
</td><td><a href="#concept-uda-input" title="concept-uda-input">input</a> is hierarchical
</td></tr><tr><td><dfn id="dom-uda-search" title="dom-uda-search"><code>search</code></dfn>
</td><td><a href="#url-query" title="url-query"><query></a>
</td><td><a href="#concept-uda-input" title="concept-uda-input">input</a> is a <a href="#hierarchical-url">hierarchical URL</a>, and contained a <a href="#url-query" title="url-query"><query></a> component (possibly an empty one)
</td><td>U+003F QUESTION MARK (?)
</td><td>—
</td><td>Remove one leading U+003F QUESTION MARK character (?), if any
</td><td><a href="#concept-uda-input" title="concept-uda-input">input</a> is a <a href="#hierarchical-url">hierarchical URL</a>
</td></tr><tr><td><dfn id="dom-uda-hash" title="dom-uda-hash"><code>hash</code></dfn>
</td><td><a href="#url-fragment" title="url-fragment"><fragment></a>
</td><td><a href="#concept-uda-input" title="concept-uda-input">input</a> contained a non-empty <a href="#url-fragment" title="url-fragment"><fragment></a> component
</td><td>U+0023 NUMBER SIGN (#)
</td><td>—
</td><td>Remove one leading U+0023 NUMBER SIGN character (#), if any
</td><td>—
</td></tr></tbody></table></div><div class="example">
<p>The table below demonstrates how the getter <span class="impl">condition</span> for <code title="dom-uda-search"><a href="#dom-uda-search">search</a></code> results in different results
depending on the exact original syntax of the URL:</p>
<table id="table-uda-examples"><thead><tr><th> Input URL
</th><th> <code title="dom-uda-search"><a href="#dom-uda-search">search</a></code> value
</th><th> Explanation
</th></tr></thead><tbody><tr><td> <code title="">http://example.com/</code>
</td><td> <i>empty string</i>
</td><td> No <a href="#url-query" title="url-query"><query></a> component in input URL.
</td></tr><tr><td> <code title="">http://example.com/?</code>
</td><td> <code title="">?</code>
</td><td> There is a <a href="#url-query" title="url-query"><query></a> component, but it is empty.
<span class="impl">The question mark in the resulting value is the prefix.</span>
</td></tr><tr><td> <code title="">http://example.com/?test</code>
</td><td> <code title="">?test</code>
</td><td> The <a href="#url-query" title="url-query"><query></a> component has the value "<code title="">test</code>".
</td></tr><tr><td> <code title="">http://example.com/?test#</code>
</td><td> <code title="">?test</code>
</td><td> The (empty) <a href="#url-fragment" title="url-fragment"><fragment></a> component is not part of the <a href="#url-query" title="url-query"><query></a> component.
</td></tr></tbody></table></div><div class="example">
<p>The following table is similar; it provides a list of what each
of the <a href="#url-decomposition-idl-attributes">URL decomposition IDL attributes</a> returns for a
given <var title="">input</var> URL.</p>
<table><thead><tr><th>Input
</th><th><code title="dom-uda-protocol"><a href="#dom-uda-protocol">protocol</a></code>
</th><th><code title="dom-uda-host"><a href="#dom-uda-host">host</a></code>
</th><th><code title="dom-uda-hostname"><a href="#dom-uda-hostname">hostname</a></code>
</th><th><code title="dom-uda-port"><a href="#dom-uda-port">port</a></code>
</th><th><code title="dom-uda-pathname"><a href="#dom-uda-pathname">pathname</a></code>
</th><th><code title="dom-uda-search"><a href="#dom-uda-search">search</a></code>
</th><th><code title="dom-uda-hash"><a href="#dom-uda-hash">hash</a></code>
</th></tr></thead><tbody><tr><td><code title="">http://example.com/carrot#question%3f</code>
</td><td><code title="">http:</code>
</td><td><code title="">example.com</code>
</td><td><code title="">example.com</code>
</td><td>(empty string)
</td><td><code title="">/carrot</code>
</td><td>(empty string)
</td><td><code title="">#question%3f</code>
</td></tr><tr><td><code title="">https://www.example.com:4443?</code>
</td><td><code title="">https:</code>
</td><td><code title="">www.example.com:4443</code>
</td><td><code title="">www.example.com</code>
</td><td><code title="">4443</code>
</td><td><code title="">/</code>
</td><td><code title="">?</code>
</td><td>(empty string)
</td></tr></tbody></table></div></body></html>