w3 parse a url

 最新链接：https://www.w3.org/TR/html53/

2.6 URLs — HTML5

li, dd li { margin: 1em 0; }
dt, dfn { font-weight: bold; font-style: normal; }
dt dfn { font-style: italic; }
pre, code { font-size: inherit; font-family: monospace; font-variant: normal; }
pre strong { color: black; font: inherit; font-weight: bold; background: yellow; }
pre em { font-weight: bolder; font-style: normal; }
@media screen { code { color: orangered; } code :link, code :visited { color: inherit; } }
var sub { vertical-align: bottom; font-size: smaller; position: relative; top: 0.1em; }
table { border-collapse: collapse; border-style: hidden hidden none hidden; }
table thead, table tbody { border-bottom: solid; }
table tbody th:first-child { border-left: solid; }
table tbody th { text-align: left; }
table td, table th { border-left: solid; border-right: solid; border-bottom: solid thin; vertical-align: top; padding: 0.2em; }
blockquote { margin: 0 0 0 2em; border: 0; padding: 0; font-style: italic; }

.bad, .bad *:not(.XXX) { color: gray; border-color: gray; background: transparent; }
.matrix, .matrix td { border: none; text-align: right; }
.matrix { margin-left: 2em; }
.dice-example { border-collapse: collapse; border-style: hidden solid solid hidden; border-width: thin; margin-left: 3em; }
.dice-example caption { width: 30em; font-size: smaller; font-style: italic; padding: 0.75em 0; text-align: left; }
.dice-example td, .dice-example th { border: solid thin; width: 1.35em; height: 1.05em; text-align: center; padding: 0; }

.toc dfn, h1 dfn, h2 dfn, h3 dfn, h4 dfn, h5 dfn, h6 dfn { font: inherit; }
img.extra { float: right; }
pre.idl { border: solid thin; background: #EEEEEE; color: black; padding: 0.5em 1em; }
pre.idl :link, pre.idl :visited { color: inherit; background: transparent; }
pre.css { border: solid thin; background: #FFFFEE; color: black; padding: 0.5em 1em; }
pre.css:first-line { color: #AAAA50; }
dl.domintro { color: green; margin: 2em 0 2em 2em; padding: 0.5em 1em; border: none; background: #DDFFDD; }
hr + dl.domintro, div.impl + dl.domintro { margin-top: 2.5em; margin-bottom: 1.5em; }
dl.domintro dt, dl.domintro dt * { color: black; text-decoration: none; }
dl.domintro dd { margin: 0.5em 0 1em 2em; padding: 0; }
dl.domintro dd p { margin: 0.5em 0; }
dl.switch { padding-left: 2em; }
dl.switch > dt { text-indent: -1.5em; }
dl.switch > dt:before { content: '\21AA'; padding: 0 0.5em 0 0; display: inline-block; width: 1em; text-align: right; line-height: 0.5em; }
dl.triple { padding: 0 0 0 1em; }
dl.triple dt, dl.triple dd { margin: 0; display: inline }
dl.triple dt:after { content: ':'; }
dl.triple dd:after { content: '\A'; white-space: pre; }
.diff-old { text-decoration: line-through; color: silver; background: transparent; }
.diff-chg, .diff-new { text-decoration: underline; color: green; background: transparent; }
a .diff-new { border-bottom: 1px blue solid; }

h2 { page-break-before: always; }
h1, h2, h3, h4, h5, h6 { page-break-after: avoid; }
h1 + h2, hr + h2.no-toc { page-break-before: auto; }

p > span:not([title=""]):not([class="XXX"]):not([class="impl"]):not([class="note"]),
li > span:not([title=""]):not([class="XXX"]):not([class="impl"]):not([class="note"]), { border-bottom: solid #9999CC; }

div.head { margin: 0 0 1em; padding: 1em 0 0 0; }
div.head p { margin: 0; }
div.head h1 { margin: 0; }
div.head .logo { float: right; margin: 0 1em; }
div.head .logo img { border: none } /* remove border from top image */
div.head dl { margin: 1em 0; }
div.head p.copyright, div.head p.alt { font-size: x-small; font-style: oblique; margin: 0; }

body > .toc > li { margin-top: 1em; margin-bottom: 1em; }
body > .toc.brief > li { margin-top: 0.35em; margin-bottom: 0.35em; }
body > .toc > li > * { margin-bottom: 0.5em; }
body > .toc > li > * > li > * { margin-bottom: 0.25em; }
.toc, .toc li { list-style: none; }

.brief { margin-top: 1em; margin-bottom: 1em; line-height: 1.1; }
.brief li { margin: 0; padding: 0; }
.brief li p { margin: 0; padding: 0; }

.category-list { margin-top: -0.75em; margin-bottom: 1em; line-height: 1.5; }
.category-list::before { content: '\21D2\A0'; font-size: 1.2em; font-weight: 900; }
.category-list li { display: inline; }
.category-list li:not(:last-child)::after { content: ', '; }
.category-list li > span, .category-list li > a { text-transform: lowercase; }
.category-list li * { text-transform: none; } /* don't affect nested in */

.XXX { color: #E50000; background: white; border: solid red; padding: 0.5em; margin: 1em 0; }
.XXX > :first-child { margin-top: 0; }
p .XXX { line-height: 3em; }
.annotation { border: solid thin black; background: #0C479D; color: white; position: relative; margin: 8px 0 20px 0; }
.annotation:before { position: absolute; left: 0; top: 0; width: 100%; height: 100%; margin: 6px -6px -6px 6px; background: #333333; z-index: -1; content: ''; }
.annotation :link, .annotation :visited { color: inherit; }
.annotation :link:hover, .annotation :visited:hover { background: transparent; }
.annotation span { border: none ! important; }
.note { color: green; background: transparent; font-family: sans-serif; }
.warning { color: red; background: transparent; }
.note, .warning { font-weight: bolder; font-style: italic; }
p.note, div.note { padding: 0.5em 2em; }
span.note { padding: 0 2em; }
.note p:first-child, .warning p:first-child { margin-top: 0; }
.note p:last-child, .warning p:last-child { margin-bottom: 0; }
.warning:before { font-style: normal; }
p.note:before { content: 'Note: '; }
p.warning:before { content: '\26A0 Warning! '; }

.bookkeeping:before { display: block; content: 'Bookkeeping details'; font-weight: bolder; font-style: italic; }
.bookkeeping { font-size: 0.8em; margin: 2em 0; }
.bookkeeping p { margin: 0.5em 2em; display: list-item; list-style: square; }
.bookkeeping dt { margin: 0.5em 2em 0; }
.bookkeeping dd { margin: 0 3em 0.5em; }

h4 { position: relative; z-index: 3; }
h4 + .element, h4 + div + .element { margin-top: -2.5em; padding-top: 2em; }
.element {
background: #EEEEFF;
color: black;
margin: 0 0 1em 0.15em;
padding: 0 1em 0.25em 0.75em;
border-left: solid #9999FF 0.25em;
position: relative;
z-index: 1;
}
.element:before {
position: absolute;
z-index: 2;
top: 0;
left: -1.15em;
height: 2em;
width: 0.9em;
background: #EEEEFF;
content: ' ';
border-style: none none solid solid;
border-color: #9999FF;
border-width: 0.25em;
}

.example { display: block; color: #222222; background: #FCFCFC; border-left: double; margin-left: 2em; padding-left: 1em; }
td > .example:only-child { margin: 0 0 0 0.1em; }

ul.domTree, ul.domTree ul { padding: 0 0 0 1em; margin: 0; }
ul.domTree li { padding: 0; margin: 0; list-style: none; position: relative; }
ul.domTree li li { list-style: none; }
ul.domTree li:first-child::before { position: absolute; top: 0; height: 0.6em; left: -0.75em; width: 0.5em; border-style: none none solid solid; content: ''; border-width: 0.1em; }
ul.domTree li:not(:last-child)::after { position: absolute; top: 0; bottom: -0.6em; left: -0.75em; width: 0.5em; border-style: none none solid solid; content: ''; border-width: 0.1em; }
ul.domTree span { font-style: italic; font-family: serif; }
ul.domTree .t1 code { color: purple; font-weight: bold; }
ul.domTree .t2 { font-style: normal; font-family: monospace; }
ul.domTree .t2 .name { color: black; font-weight: bold; }
ul.domTree .t2 .value { color: blue; font-weight: normal; }
ul.domTree .t3 code, .domTree .t4 code, .domTree .t5 code { color: gray; }
ul.domTree .t7 code, .domTree .t8 code { color: green; }
ul.domTree .t10 code { color: teal; }

body.dfnEnabled dfn { cursor: pointer; }
.dfnPanel {
display: inline;
position: absolute;
z-index: 10;
height: auto;
width: auto;
padding: 0.5em 0.75em;
font: small sans-serif, Droid Sans Fallback;
background: #DDDDDD;
color: black;
border: outset 0.2em;
}
.dfnPanel * { margin: 0; padding: 0; font: inherit; text-indent: 0; }
.dfnPanel :link, .dfnPanel :visited { color: black; }
.dfnPanel p { font-weight: bolder; }
.dfnPanel * + p { margin-top: 0.25em; }
.dfnPanel li { list-style-position: inside; }

#configUI { position: absolute; z-index: 20; top: 10em; right: 1em; width: 11em; font-size: small; }
#configUI p { margin: 0.5em 0; padding: 0.3em; background: #EEEEEE; color: black; border: inset thin; }
#configUI p label { display: block; }
#configUI #updateUI, #configUI .loginUI { text-align: center; }
#configUI input[type=button] { display: block; margin: auto; }

fieldset { margin: 1em; padding: 0.5em 1em; }
fieldset > legend + * { margin-top: 0; }
fieldset > :last-child { margin-bottom: 0; }
fieldset p { margin: 0.5em 0; }

.stability {
position: fixed;
bottom: 0;
left: 0; right: 0;
margin: 0 auto 0 auto !important;
z-index: 1000;
width: 50%;
background: maroon; color: yellow;
-webkit-border-radius: 1em 1em 0 0;
-moz-border-radius: 1em 1em 0 0;
border-radius: 1em 1em 0 0;
-moz-box-shadow: 0 0 1em #500;
-webkit-box-shadow: 0 0 1em #500;
box-shadow: 0 0 1em red;
padding: 0.5em 1em;
text-align: center;
}
.stability strong {
display: block;
}
.stability input {
appearance: none; margin: 0; border: 0; padding: 0.25em 0.5em; background: transparent; color: black;
position: absolute; top: -0.5em; right: 0; font: 1.25em sans-serif; text-align: center;
}
.stability input:hover {
color: white;
text-shadow: 0 0 2px black;
}
.stability input:active {
padding: 0.3em 0.45em 0.2em 0.55em;
}
.stability :link, .stability :visited,
.stability :link:hover, .stability :visited:hover {
background: transparent;
color: white;
}
-->
* { display: block; }
.applies thead code { display: block; }
.applies tbody th { whitespace: nowrap; }
.applies td { text-align: center; }
.applies .yes { background: yellow; }

.matrix, .matrix td { border: hidden; text-align: right; }
.matrix { margin-left: 2em; }

.dice-example { border-collapse: collapse; border-style: hidden solid solid hidden; border-width: thin; margin-left: 3em; }
.dice-example caption { width: 30em; font-size: smaller; font-style: italic; padding: 0.75em 0; text-align: left; }
.dice-example td, .dice-example th { border: solid thin; width: 1.35em; height: 1.05em; text-align: center; padding: 0; }

td.eg { border-width: thin; text-align: center; }

#table-example-1 { border: solid thin; border-collapse: collapse; margin-left: 3em; }
#table-example-1 * { font-family: "Essays1743", serif; line-height: 1.01em; }
#table-example-1 caption { padding-bottom: 0.5em; }
#table-example-1 thead, #table-example-1 tbody { border: none; }
#table-example-1 th, #table-example-1 td { border: solid thin; }
#table-example-1 th { font-weight: normal; }
#table-example-1 td { border-style: none solid; vertical-align: top; }
#table-example-1 th { padding: 0.5em; vertical-align: middle; text-align: center; }
#table-example-1 tbody tr:first-child td { padding-top: 0.5em; }
#table-example-1 tbody tr:last-child td { padding-bottom: 1.5em; }
#table-example-1 tbody td:first-child { padding-left: 2.5em; padding-right: 0; width: 9em; }
#table-example-1 tbody td:first-child::after { content: leader(". "); }
#table-example-1 tbody td { padding-left: 2em; padding-right: 2em; }
#table-example-1 tbody td:first-child + td { width: 10em; }
#table-example-1 tbody td:first-child + td ~ td { width: 2.5em; }
#table-example-1 tbody td:first-child + td + td + td ~ td { width: 1.25em; }

.apple-table-examples { border: none; border-collapse: separate; border-spacing: 1.5em 0em; width: 40em; margin-left: 3em; }
.apple-table-examples * { font-family: "Times", serif; }
.apple-table-examples td, .apple-table-examples th { border: none; white-space: nowrap; padding-top: 0; padding-bottom: 0; }
.apple-table-examples tbody th:first-child { border-left: none; width: 100%; }
.apple-table-examples thead th:first-child ~ th { font-size: smaller; font-weight: bolder; border-bottom: solid 2px; text-align: center; }
.apple-table-examples tbody th::after, .apple-table-examples tfoot th::after { content: leader(". ") }
.apple-table-examples tbody th, .apple-table-examples tfoot th { font: inherit; text-align: left; }
.apple-table-examples td { text-align: right; vertical-align: top; }
.apple-table-examples.e1 tbody tr:last-child td { border-bottom: solid 1px; }
.apple-table-examples.e1 tbody + tbody tr:last-child td { border-bottom: double 3px; }
.apple-table-examples.e2 th[scope=row] { padding-left: 1em; }
.apple-table-examples sup { line-height: 0; }

.details-example img { vertical-align: top; }

#base64-table {
white-space: nowrap;
font-size: 0.6em;
column-width: 6em;
column-count: 5;
column-gap: 1em;
-moz-column-width: 6em;
-moz-column-count: 5;
-moz-column-gap: 1em;
-webkit-column-width: 6em;
-webkit-column-count: 5;
-webkit-column-gap: 1em;
}
#base64-table thead { display: none; }
#base64-table * { border: none; }
#base64-table tbody td:first-child:after { content: ':'; }
#base64-table tbody td:last-child { text-align: right; }

#named-character-references-table {
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; }
#named-character-references-table > table > tbody > tr > td:last-child:hover > span { position: absolute; top: auto; left: auto; margin-left: 0.5em; line-height: 1.2; font-size: 5em; border: outset; padding: 0.25em 0.5em; background: white; width: 1.25em; height: auto; text-align: center; }
#named-character-references-table > table > tbody > tr#entity-CounterClockwiseContourIntegral > td:first-child { font-size: 0.5em; }

.glyph.control { color: red; }

@font-face {
font-family: 'Essays1743';
src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743.ttf');
}
@font-face {
font-family: 'Essays1743';
font-weight: bold;
src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743-Bold.ttf');
}
@font-face {
font-family: 'Essays1743';
font-style: italic;
src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743-Italic.ttf');
}
@font-face {
font-family: 'Essays1743';
font-style: italic;
font-weight: bold;
src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743-BoldItalic.ttf');
}
-->

This is a work in progress! For the latest updates from the HTML WG, possibly including important bug fixes, please look at the editor's draft instead. There may also be a more up-to-date Working Draft with changes based on resolution of Last Call issues.

HTML5

2.5 Common microsyntaxes – Table of contents – 2.7 Fetching resources

1. 1. 2.6 URLs
      1. 2.6.1 Terminology
      2. 2.6.2 Parsing URLs
      3. 2.6.3 Resolving URLs
      4. 2.6.4 URL manipulation and creation
      5. 2.6.5 Dynamic changes to base URLs
      6. 2.6.6 Interfaces for URL manipulation

2.6 URLs

This specification defines the term URL, 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.

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 this specification if they pretend the term "URL" as used herein is really called something else altogether. This is a willful violation of RFC 3986. [RFC3986]

2.6.1 Terminology

A URL is a string used to identify a resource.

A URL is a valid URL if at least one of the following conditions holds:

• The URL is a valid URI reference [RFC3986].

• The URL is a valid IRI reference and it has no query component. [RFC3987]

• The URL is a valid IRI reference and its query component contains no unescaped non-ASCII characters. [RFC3987]

• The URL is a valid IRI reference and the character encoding of the URL's Document is UTF-8 or UTF-16. [RFC3987]

A string is a valid non-empty URL if it is a valid URL but it is not the empty string.

A string is a valid URL potentially surrounded by spaces if, after stripping leading and trailing whitespace from it, it is a valid URL.

A string is a valid non-empty URL potentially surrounded by spaces if, after stripping leading and trailing whitespace from it, it is a valid non-empty URL.

This specification defines the URL about:legacy-compat as a reserved, though unresolvable, about: URI, for use in DOCTYPEs in HTML documents when needed for compatibility with XML tools. [ABOUT]

This specification defines the URL about:srcdoc as a reserved, though unresolvable, about: URI, that is used as the document's address of iframe srcdoc documents. [ABOUT]

2.6.2 Parsing URLs

To parse a URL url into its component parts, the user agent must use the following steps:

1. Strip leading and trailing space characters from url.

2. Parse url in the manner defined by RFC 3986, with the following exceptions:

   • 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.
   • Add the characters U+0022, U+003C, U+003E, U+005B .. U+005E, U+0060, and U+007B .. U+007D to the <unreserved> production.
   • 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.
   • Add the U+0023 NUMBER SIGN character to the characters allowed in the <fragment> production.

3. If url 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. [RFC3986]

   Otherwise, parsing url was successful; the components of the URL are substrings of url defined as follows:

   <scheme>

   The substring matched by the <scheme> production, if any.

   <host>

   The substring matched by the <host> production, if any.

   <port>

   The substring matched by the <port> production, if any.

   <hostport>

   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.

   <path>

   The substring matched by one of the following productions, if one of them was matched:

   • <path-abempty>
   • <path-absolute>
   • <path-noscheme>
   • <path-rootless>
   • <path-empty>

   <query>

   The substring matched by the <query> production, if any.

   <fragment>

   The substring matched by the <fragment> production, if any.

   <host-specific>

   The substring that follows the substring matched by the <authority> production, or the whole string if the <authority> production wasn't matched.

These parsing rules are a willful violation of RFC 3986 and RFC 3987 (which do not define error handling), motivated by a desire to handle legacy content. [RFC3986] [RFC3987]

2.6.3 Resolving URLs

Resolving a URL is the process of taking a relative URL and obtaining the absolute URL that it implies.

To resolve a URL to an absolute URL relative to either another absolute URL 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.

1. Let url be the URL being resolved.

2. Let encoding be determined as follows:

   If the URL had a character encoding defined when the URL was created or defined

   The URL character encoding is as defined.

   If the URL came from a script (e.g. as an argument to a method)

   The URL character encoding is the script's URL character encoding.

   If the URL came from a DOM node (e.g. from an element)

   The node has a Document, and the URL character encoding is the document's character encoding.

3. If encoding is a UTF-16 encoding, then change the value of encoding to UTF-8.

4. If the algorithm was invoked with an absolute URL to use as the base URL, let base be that absolute URL.

   Otherwise, let base be the base URI of the element, as defined by the XML Base specification, with the base URI of the document entity being defined as the document base URL of the Document that owns the element. [XMLBASE]

   For the purposes of the XML Base specification, user agents must act as if all Document objects represented XML documents.

   It is possible for xml:base 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 xml:base attributes are not allowed in HTML documents.)

   The document base URL of a Document object is the absolute URL obtained by running these substeps:

   1. Let fallback base url be the document's address.

   2. If fallback base url is about:blank, and the Document's browsing context has a creator browsing context, then let fallback base url be the document base URL of the creator Document instead.

   3. If the Document is an iframe srcdoc document, then let fallback base url be the document base URL of the Document's browsing context's browsing context container's Document instead.

   4. If there is no base element that has an href attribute, then the document base URL is fallback base url; abort these steps. Otherwise, let url be the value of the href attribute of the first such element.

   5. Resolve url relative to fallback base url (thus, the base href attribute isn't affected by xml:base attributes).

   6. The document base URL is the result of the previous step if it was successful; otherwise it is fallback base url.

5. Parse url into its component parts.

6. If parsing url resulted in a <host> component, then replace the matching substring of url 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.

   If any percent-encoded octets in that component are not valid UTF-8 sequences, then return an error and abort these steps.

   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.

   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. [RFC3490]

7. If parsing url resulted in a <path> component, then replace the matching substring of url 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:

   1. Encode the character into a sequence of octets as defined by UTF-8.
   2. Replace the character with the percent-encoded form of those octets. [RFC3986]

   For instance if url was "//example.com/a^b☺c%FFd%z/?e", then the <path> component's substring would be "/a^b☺c%FFd%z/" and the two characters that would have to be escaped would be "^" and "☺". The result after this step was applied would therefore be that url now had the value "//example.com/a%5Eb%E2%98%BAc%FFd%z/?e".

8. If parsing url resulted in a <query> component, then replace the matching substring of url 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:

   1. If the character in question cannot be expressed in the encoding encoding, then replace it with a single 0x3F octet (an ASCII question mark) and skip the remaining substeps for this character.
   2. Encode the character into a sequence of octets as defined by the encoding encoding.
   3. Replace the character with the percent-encoded form of those octets. [RFC3986]

9. Apply the algorithm described in RFC 3986 section 5.2 Relative Resolution, using url as the potentially relative URI reference (R), and base as the base URI (Base). [RFC3986]

10. Apply any relevant conformance criteria of RFC 3986 and RFC 3987, returning an error and aborting these steps if appropriate. [RFC3986] [RFC3987]

    For instance, if an absolute URI that would be returned by the above algorithm violates the restrictions specific to its scheme, e.g. a data: URI using the "//" server-based naming authority syntax, then user agents are to treat this as an error instead.

11. Let result be the target URI (T) returned by the Relative Resolution algorithm.

12. If result uses a scheme with a server-based naming authority, replace all U+005C REVERSE SOLIDUS (\) characters in result with U+002F SOLIDUS (/) characters.

13. Return result.

Some of the steps in these rules, for example the processing of U+005C REVERSE SOLIDUS (\) characters, are a willful violation of RFC 3986 and RFC 3987, motivated by a desire to handle legacy content. [RFC3986] [RFC3987]

A URL is an absolute URL if resolving it results in the same output regardless of what it is resolved relative to, and that output is not a failure.

An absolute URL is a hierarchical URL if, when resolved and then parsed, there is a character immediately after the <scheme> component and it is a U+002F SOLIDUS character (/).

An absolute URL is an authority-based URL if, when resolved and then parsed, there are two characters immediately after the <scheme> component and they are both U+002F SOLIDUS characters (//).

2.6.4 URL manipulation and creation

To fragment-escape a string input, a user agent must run the following steps:

1. Let input be the string to be escaped.

2. Let position point at the first character of input.

3. Let output be an empty string.

4. Loop: If position is past the end of input, then jump to the step labeled end.

5. If the character in input pointed to by position is in the range U+0000 to U+0020 or is one of the following characters:

   • U+0022 QUOTATION MARK character (")
   • U+0023 NUMBER SIGN character (#)
   • U+0025 PERCENT SIGN character (%)
   • U+003C LESS-THAN SIGN character (<)
   • U+003E GREATER-THAN SIGN character (>)
   • U+005B LEFT SQUARE BRACKET character ([)
   • U+005C REVERSE SOLIDUS character (\)
   • U+005D RIGHT SQUARE BRACKET character (])
   • U+005E CIRCUMFLEX ACCENT character (^)
   • U+007B LEFT CURLY BRACKET character ({)
   • U+007C VERTICAL LINE character (|)
   • U+007D RIGHT CURLY BRACKET character (})

   ...then append the percent-encoded form of the character to output. [RFC3986]

   Otherwise, append the character itself to output.

   This escapes any ASCII characters that are not valid in the URI <fragment> production without being escaped.

6. Advance position to the next character in input.

7. Return to the step labeled loop.

8. End: Return output.

2.6.5 Dynamic changes to base URLs

When an xml:base attribute changes, the attribute's element, and all descendant elements, are affected by a base URL change.

When a document's document base URL changes, all elements in that document are affected by a base URL change.

When an element is moved from one document to another, if the two documents have different base URLs, then that element and all its descendants are affected by a base URL change.

When an element is affected by a base URL change, it must act as described in the following list:

If the element creates a hyperlink

If the absolute URL identified by the hyperlink is being shown to the user, or if any data derived from that URL is affecting the display, then the href attribute should be re-resolved relative to the element and the UI updated appropriately.

For example, the CSS :link/:visited pseudo-classes might have been affected.

If the element is a q, blockquote, section, article, ins, or del element with a cite attribute

If the absolute URL identified by the cite attribute is being shown to the user, or if any data derived from that URL is affecting the display, then the URL should be re-resolved relative to the element and the UI updated appropriately.

Otherwise

The element is not directly affected.

Changing the base URL doesn't affect the image displayed by img elements, although subsequent accesses of the src IDL attribute from script will return a new absolute URL that might no longer correspond to the image being shown.

2.6.6 Interfaces for URL manipulation

An interface that has a complement of URL decomposition IDL attributes has seven attributes with the following definitions:

           attribute DOMString protocol;
           attribute DOMString host;
           attribute DOMString hostname;
           attribute DOMString port;
           attribute DOMString pathname;
           attribute DOMString search;
           attribute DOMString hash;

o . protocol [ = value ]

Returns the current scheme of the underlying URL.

Can be set, to change the underlying URL's scheme.

o . host [ = value ]

Returns the current host and port (if it's not the default port) in the underlying URL.

Can be set, to change the underlying URL's host and port.

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.

o . hostname [ = value ]

Returns the current host in the underlying URL.

Can be set, to change the underlying URL's host.

o . port [ = value ]

Returns the current port in the underlying URL.

Can be set, to change the underlying URL's port.

o . pathname [ = value ]

Returns the current path in the underlying URL.

Can be set, to change the underlying URL's path.

o . search [ = value ]

Returns the current query component in the underlying URL.

Can be set, to change the underlying URL's query component.

o . hash [ = value ]

Returns the current fragment identifier in the underlying URL.

Can be set, to change the underlying URL's fragment identifier.

---

The attributes defined to be URL decomposition IDL attributes must act as described for the attributes with the same corresponding names in this section.

In addition, an interface with a complement of URL decomposition IDL attributes defines an input, which is a URL that the attributes act on, and a common setter action, which is a set of steps invoked when any of the attributes' setters are invoked.

The seven URL decomposition IDL attributes have similar requirements.

On getting, if the input is an absolute URL 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 input 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.

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 input is an absolute URL and the resulting new value fulfills the condition given in the "setter condition" column, the user agent must make a new string output by replacing the component of the URL given by the "component" column in the input URL with the new value; otherwise, the user agent must let output be equal to the input. Finally, the user agent must invoke the common setter action with the value of output.

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.

The previous paragraph applies in particular to the ":" before a <port> component, the "?" before a <query> component, and the "#" before a <fragment> component.

For the purposes of the above definitions, URLs must be parsed using the URL parsing rules defined in this specification.

Attribute	Component	Getter Condition	Prefix	Suffix	Setter Preprocessor	Setter Condition
protocol	<scheme>	—	—	U+003A COLON (:)	Remove all trailing U+003A COLON characters (:)	The new value is not the empty string
host	<hostport>	input is an authority-based URL	—	—	—	The new value is not the empty string and input is an authority-based URL
hostname	<host>	input is an authority-based URL	—	—	Remove all leading U+002F SOLIDUS characters (/)	The new value is not the empty string and input is an authority-based URL
port	<port>	input is an authority-based URL, and contained a <port> component (possibly an empty one)	—	—	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).	input is an authority-based URL, and the new value, when interpreted as a base-ten integer, is less than or equal to 65535
pathname	<path>	input is a hierarchical URL	—	—	If it has no leading U+002F SOLIDUS character (/), prepend a U+002F SOLIDUS character (/) to the new value	input is hierarchical
search	<query>	input is a hierarchical URL, and contained a <query> component (possibly an empty one)	U+003F QUESTION MARK (?)	—	Remove one leading U+003F QUESTION MARK character (?), if any	input is a hierarchical URL
hash	<fragment>	input contained a non-empty <fragment> component	U+0023 NUMBER SIGN (#)	—	Remove one leading U+0023 NUMBER SIGN character (#), if any	—

The table below demonstrates how the getter condition for search results in different results depending on the exact original syntax of the URL:

Input URL	search value	Explanation
http://example.com/	empty string	No <query> component in input URL.
http://example.com/?	?	There is a <query> component, but it is empty. The question mark in the resulting value is the prefix.
http://example.com/?test	?test	The <query> component has the value "test".
http://example.com/?test#	?test	The (empty) <fragment> component is not part of the <query> component.

The following table is similar; it provides a list of what each of the URL decomposition IDL attributes returns for a given input URL.

Input	protocol	host	hostname	port	pathname	search	hash
http://example.com/carrot#question%3f	http:	example.com	example.com	(empty string)	/carrot	(empty string)	#question%3f
https://www.example.com:4443?	https:	www.example.com:4443	www.example.com	4443	/	?	(empty string)

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	</head><body><div class="head" id="head">
	<div id="multipage-common">
	<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.
	There may also be a more
	<a href="http://www.w3.org/TR/html5">up-to-date Working Draft</a>
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	<p><a href="http://www.w3.org/"><img alt="W3C" height="48" src="http://www.w3.org/Icons/w3c_home" width="72"></a></p>
	<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
	&lt;unreserved&gt; 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 &lt;unreserved&gt;
	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 &lt;pct-encoded&gt; production,
	except when the &lt;pct-encoded&gt; is used in the
	&lt;reg-name&gt; production.</li>
	<li>Add the U+0023 NUMBER SIGN character to the characters
	allowed in the &lt;fragment&gt; production.</li>
	</ul></li>
	<li>
	<p>If <var title="">url</var> doesn't match the
	&lt;URI-reference&gt; 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">&lt;scheme&gt;</dfn></dt>
	<dd><p>The substring matched by the &lt;scheme&gt; production, if any.</p></dd>
	<dt><dfn id="url-host" title="url-host">&lt;host&gt;</dfn></dt>
	<dd><p>The substring matched by the &lt;host&gt; production, if any.</p></dd>
	<dt><dfn id="url-port" title="url-port">&lt;port&gt;</dfn></dt>
	<dd><p>The substring matched by the &lt;port&gt; production, if any.</p></dd>
	<dt><dfn id="url-hostport" title="url-hostport">&lt;hostport&gt;</dfn></dt>
	<dd><p>If there is a &lt;scheme&gt; component and a &lt;port&gt;
	component and the port given by the &lt;port&gt; component is
	different than the default port defined for the protocol given by
	the &lt;scheme&gt; component, then &lt;hostport&gt; is the
	substring that starts with the substring matched by the
	&lt;host&gt; production and ends with the substring matched by the
	&lt;port&gt; production, and includes the colon in between the
	two. Otherwise, it is the same as the &lt;host&gt; component.</p>
	</dd><dt><dfn id="url-path" title="url-path">&lt;path&gt;</dfn></dt>
	<dd>
	<p>The substring matched by one of the following productions, if
	one of them was matched:</p>
	<ul class="brief"><li>&lt;path-abempty&gt;</li>
	<li>&lt;path-absolute&gt;</li>
	<li>&lt;path-noscheme&gt;</li>
	<li>&lt;path-rootless&gt;</li>
	<li>&lt;path-empty&gt;</li>
	</ul></dd>
	<dt><dfn id="url-query" title="url-query">&lt;query&gt;</dfn></dt>
	<dd><p>The substring matched by the &lt;query&gt; production, if any.</p></dd>
	<dt><dfn id="url-fragment" title="url-fragment">&lt;fragment&gt;</dfn></dt>
	<dd><p>The substring matched by the &lt;fragment&gt; production, if any.</p></dd>
	<dt><dfn id="url-host-specific" title="url-host-specific">&lt;host-specific&gt;</dfn></dt>
	<dd><p>The substring that <em>follows</em> the substring matched
	by the &lt;authority&gt; production, or the whole string if the
	&lt;authority&gt; 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">&lt;host&gt;</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">&lt;path&gt;</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
	&lt;path&gt; 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">&lt;path&gt;</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">&lt;query&gt;</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
	&lt;query&gt; 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">&lt;scheme&gt;</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">&lt;scheme&gt;</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 (&lt;)
	</li><li>U+003E GREATER-THAN SIGN character (&gt;)
	</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 &lt;fragment&gt; 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 &lt;port&gt; component, the "<code title="">?</code>" before a &lt;query&gt; component, and the "<code title="">#</code>" before a &lt;fragment&gt; 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">&lt;scheme&gt;</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">&lt;hostport&gt;</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">&lt;host&gt;</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">&lt;port&gt;</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">&lt;port&gt;</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">&lt;path&gt;</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">&lt;query&gt;</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">&lt;query&gt;</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">&lt;fragment&gt;</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">&lt;fragment&gt;</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">&lt;query&gt;</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">&lt;query&gt;</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">&lt;query&gt;</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">&lt;fragment&gt;</a> component is not part of the <a href="#url-query" title="url-query">&lt;query&gt;</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>