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<pre class="metadata">
Group: WHATWG
H1: URL Pattern
Shortname: urlpattern
Text Macro: TWITTER urlpatterns
Text Macro: LATESTRD 2024-03
Abstract: The URL Pattern Standard provides a web platform primitive for matching URLs based on a convenient pattern syntax.
Indent: 2
Markup Shorthands: markdown yes
Translation: zh-Hans https://htmlspecs.com/urlpattern/
Required IDs: url-pattern,url-pattern-create,url-pattern-match,url-pattern-has-regexp-groups
</pre>
<pre class="link-defaults">
spec:infra; type:dfn; text:list
spec:webidl; type:dfn; text:record
</pre>
<pre class="anchors">
spec: ECMASCRIPT; urlPrefix: https://tc39.es/ecma262/
type: dfn
text: IdentifierPart; url: #prod-IdentifierPart
text: IdentifierStart; url: #prod-IdentifierStart
spec: URL; urlPrefix: https://url.spec.whatwg.org/
type: dfn
text: serialize an integer; url: #serialize-an-integer
text: host serializer; url: #concept-host-serializer
spec: RFC9651; urlPrefix: https://httpwg.org/specs/rfc9651.html
type: dfn
text: structured header; url: top
for: structured header
text: string; url: string
</pre>
<h2 id=urlpatterns>URL patterns</h2>
<h3 id=introduction>Introduction</h3>
A [=URL pattern=] consists of several [=components=], each of which represents a [=/pattern string|pattern=] which could be matched against the corresponding component of a [=/URL=].
It can be constructed using a string for each component, or from a [[#constructor-string-parsing|shorthand string]]. It can optionally be resolved relative to a base URL.
<div class="example" id="example-intro">
<p>The shorthand "`https://example.com/:category/*`" corresponds to the following components:
<dl class="props">
<dt>[=URL pattern/protocol component|protocol=]
<dd>"`https`"
<dt>[=URL pattern/username component|username=]
<dd>"`*`"
<dt>[=URL pattern/password component|password=]
<dd>"`*`"
<dt>[=URL pattern/hostname component|hostname=]
<dd>"`example.com`"
<dt>[=URL pattern/port component|port=]
<dd>""
<dt>[=URL pattern/pathname component|pathname=]
<dd>"`/:category/*`"
<dt>[=URL pattern/search component|search=]
<dd>"`*`"
<dt>[=URL pattern/hash component|hash=]
<dd>"`*`"
</dl>
It matches the following URLs:
<ul class="brief">
* `https://example.com/products/`
* `https://example.com/blog/our-greatest-product-ever`
</ul>
It does not match the following URLs:
<ul class="brief">
* `https://example.com/`
* `http://example.com/products/`
* `https://example.com:8443/blog/our-greatest-product-ever`
</ul>
This is a fairly simple pattern which requires most components to either match an exact string, or allows any string ("`*`"). The [=URL pattern/pathname component=] matches any path with at least two `/`-separated path components, the first of which is captured as "`category`".
</div>
<div class="example" id="example-intro-2">
<p>The shorthand "`http{s}?://{:subdomain.}?shop.example/products/:id([0-9]+)#reviews`" corresponds to the following components:
<dl class="props">
<dt>[=URL pattern/protocol component|protocol=]
<dd>"`http{s}?`"
<dt>[=URL pattern/username component|username=]
<dd>"`*`"
<dt>[=URL pattern/password component|password=]
<dd>"`*`"
<dt>[=URL pattern/hostname component|hostname=]
<dd>"`{:subdomain.}?shop.example`"
<dt>[=URL pattern/port component|port=]
<dd>""
<dt>[=URL pattern/pathname component|pathname=]
<dd>"`/products/:id([0-9]+)`"
<dt>[=URL pattern/search component|search=]
<dd>""
<dt>[=URL pattern/hash component|hash=]
<dd>"`reviews`"
</dl>
It matches the following URLs:
<ul class="brief">
* `https://shop.example/products/74205#reviews`
* `https://[email protected]/products/74656#reviews`
* `http://insecure.shop.example/products/1701#reviews`
</ul>
It does not match the following URLs:
<ul class="brief">
* `https://shop.example/products/2000`
* `http://shop.example:8080/products/0#reviews`
* `https://nx.shop.example/products/01?speed=5#reviews`
* `https://shop.example/products/chair#reviews`
</ul>
This is a more complicated pattern which includes:
* <a for=part/modifier><span class="allow-2119">optional</span></a> parts marked with `?` (braces are needed to make it unambiguous exactly what is <span class="allow-2119">optional</span>), and
* a [=part/type/regexp=] part named "`id`" which uses a regular expression to define what sorts of substrings match (the parentheses are necessary to mark it as a regular expression, and are not part of the regexp itself).
</div>
<div class="example" id="example-intro-3">
<p>The shorthand "`../admin/*`" with the base URL "`https://discussion.example/forum/?page=2`" corresponds to the following components:
<dl class="props">
<dt>[=URL pattern/protocol component|protocol=]
<dd>"`https`"
<dt>[=URL pattern/username component|username=]
<dd>"`*`"
<dt>[=URL pattern/password component|password=]
<dd>"`*`"
<dt>[=URL pattern/hostname component|hostname=]
<dd>"`discussion.example`"
<dt>[=URL pattern/port component|port=]
<dd>""
<dt>[=URL pattern/pathname component|pathname=]
<dd>"`/admin/*`"
<dt>[=URL pattern/search component|search=]
<dd>"`*`"
<dt>[=URL pattern/hash component|hash=]
<dd>"`*`"
</dl>
It matches the following URLs:
<ul class="brief">
* `https://discussion.example/admin/`
* `https://edd:[email protected]/admin/update?id=1`
</ul>
It does not match the following URLs:
<ul class="brief">
* `https://discussion.example/forum/admin/`
* `http://discussion.example:8080/admin/update?id=1`
</ul>
This pattern demonstrates how pathnames are resolved relative to a base URL, in a similar way to relative URLs.
</div>
<h3 id=urlpattern-class>The {{URLPattern}} class</h3>
<xmp class="idl">
typedef (USVString or URLPatternInit) URLPatternInput;
[Exposed=(Window,Worker)]
interface URLPattern {
constructor(URLPatternInput input, USVString baseURL, optional URLPatternOptions options = {});
constructor(optional URLPatternInput input = {}, optional URLPatternOptions options = {});
boolean test(optional URLPatternInput input = {}, optional USVString baseURL);
URLPatternResult? exec(optional URLPatternInput input = {}, optional USVString baseURL);
readonly attribute USVString protocol;
readonly attribute USVString username;
readonly attribute USVString password;
readonly attribute USVString hostname;
readonly attribute USVString port;
readonly attribute USVString pathname;
readonly attribute USVString search;
readonly attribute USVString hash;
readonly attribute boolean hasRegExpGroups;
};
dictionary URLPatternInit {
USVString protocol;
USVString username;
USVString password;
USVString hostname;
USVString port;
USVString pathname;
USVString search;
USVString hash;
USVString baseURL;
};
dictionary URLPatternOptions {
boolean ignoreCase = false;
};
dictionary URLPatternResult {
sequence<URLPatternInput> inputs;
URLPatternComponentResult protocol;
URLPatternComponentResult username;
URLPatternComponentResult password;
URLPatternComponentResult hostname;
URLPatternComponentResult port;
URLPatternComponentResult pathname;
URLPatternComponentResult search;
URLPatternComponentResult hash;
};
dictionary URLPatternComponentResult {
USVString input;
record<USVString, (USVString or undefined)> groups;
};
</xmp>
Each {{URLPattern}} has an <dfn for="URLPattern">associated URL pattern</dfn>, a [=URL pattern=].
<dl class="domintro non-normative">
<dt><code>|urlPattern| = new {{URLPattern/constructor(input, baseURL, options)|URLPattern}}(|input|)</code></dt>
<dd>
Constructs a new {{URLPattern}} object. The |input| is an object containing separate patterns for each URL component; e.g. hostname, pathname, etc. Missing components will default to a wildcard pattern. In addition, |input| can contain a {{URLPatternInit/baseURL}} property that provides static text patterns for any missing components.
</dd>
<dt><code>|urlPattern| = new {{URLPattern/constructor(input, baseURL, options)|URLPattern}}(|patternString|, |baseURL|)</code></dt>
<dd>
Constructs a new {{URLPattern}} object. |patternString| is a URL string containing pattern syntax for one or more components. If |baseURL| is provided, then |patternString| can be relative. This constructor will always set at least an empty string value and does not default any components to wildcard patterns.
</dd>
<dt><code>|urlPattern| = new {{URLPattern/constructor(input, baseURL, options)|URLPattern}}(|input|, |options|)</code></dt>
<dd>
Constructs a new {{URLPattern}} object. The |options| is an object containing the additional configuration options that can affect how the components are matched. Currently it has only one property {{URLPatternOptions/ignoreCase}} which can be set to true to enable case-insensitive matching.
Note that by default, that is in the absence of the |options| argument, matching is always case-sensitive.
</dd>
<dt><code>|urlPattern| = new {{URLPattern/constructor(input, baseURL, options)|URLPattern}}(|patternString|, |baseURL|, |options|)</code></dt>
<dd>
Constructs a new {{URLPattern}} object. This overrides supports a {{URLPatternOptions}} object when constructing a pattern from a |patternString| object, describing the patterns for individual components, and base URL.
</dd>
<dt><code>|matches| = |urlPattern|.{{URLPattern/test(input, baseURL)|test}}(|input|)</code></dt>
<dd>
Tests if |urlPattern| matches the given arguments. The |input| is an object containing strings representing each URL component; e.g. hostname, pathname, etc. Missing components are treated as empty strings. In addition, |input| can contain a {{URLPatternInit/baseURL}} property that provides values for any missing components. If |urlPattern| matches the |input| on a component-by-component basis then true is returned. Otherwise, false is returned.
</dd>
<dt><code>|matches| = |urlPattern|.{{URLPattern/test(input, baseURL)|test}}(|url|, |baseURL|)</code></dt>
<dd>
Tests if |urlPattern| matches the given arguments. |url| is a URL string. If |baseURL| is provided, then |url| can be relative.
If |urlPattern| matches the |input| on a component-by-component basis then true is returned. Otherwise, false is returned.
</dd>
<dt><code>|result| = |urlPattern|.{{URLPattern/exec(input, baseURL)|exec}}(|input|)</code></dt>
<dd>
Executes the |urlPattern| against the given arguments. The |input| is an object containing strings representing each URL component; e.g. hostname, pathname, etc. Missing components are treated as empty strings. In addition, |input| can contain a baseURL property that provides values for any missing components.
If |urlPattern| matches the |input| on a component-by-component basis then an object is returned containing the results. Matched group values are contained in per-component group objects within the |result| object; e.g. `matches.pathname.groups.id`. If |urlPattern| does not match the |input|, then |result| is null.
</dd>
<dt><code>|result| = |urlPattern|.{{URLPattern/exec(input, baseURL)|exec}}(|url|, |baseURL|)</code></dt>
<dd>
Executes the |urlPattern| against the given arguments. |url| is a URL string. If |baseURL| is provided, then |input| can be relative.
If |urlPattern| matches the |input| on a component-by-component basis then an object is returned containing the results. Matched group values are contained in per-component group objects within the |result| object; e.g. `matches.pathname.groups.id`. If |urlPattern| does not match the |input|, then |result| is null.
</dd>
<dt><code>|urlPattern|.{{URLPattern/protocol}}</code></dt>
<dd>
<p>Returns |urlPattern|'s normalized protocol pattern string.
</dd>
<dt><code>|urlPattern|.{{URLPattern/username}}</code></dt>
<dd>
<p>Returns |urlPattern|'s normalized username pattern string.
</dd>
<dt><code>|urlPattern|.{{URLPattern/password}}</code></dt>
<dd>
<p>Returns |urlPattern|'s normalized password pattern string.
</dd>
<dt><code>|urlPattern|.{{URLPattern/hostname}}</code></dt>
<dd>
<p>Returns |urlPattern|'s normalized hostname pattern string.
</dd>
<dt><code>|urlPattern|.{{URLPattern/port}}</code></dt>
<dd>
<p>Returns |urlPattern|'s normalized port pattern string.
</dd>
<dt><code>|urlPattern|.{{URLPattern/pathname}}</code></dt>
<dd>
<p>Returns |urlPattern|'s normalized pathname pattern string.
</dd>
<dt><code>|urlPattern|.{{URLPattern/search}}</code></dt>
<dd>
<p>Returns |urlPattern|'s normalized search pattern string.
</dd>
<dt><code>|urlPattern|.{{URLPattern/hash}}</code></dt>
<dd>
<p>Returns |urlPattern|'s normalized hash pattern string.
</dd>
<dt><code>|urlPattern|.{{URLPattern/hasRegExpGroups}}</code></dt>
<dd>
<p>Returns whether |urlPattern| contains one or more groups which uses regular expression matching.
</dd>
</dl>
<div algorithm>
The <dfn constructor for=URLPattern lt="URLPattern(input, baseURL, options)">new URLPattern(|input|, |baseURL|, |options|)</dfn> constructor steps are:
1. Run [=initialize=] given [=this=], |input|, |baseURL|, and |options|.
</div>
<div algorithm>
The <dfn constructor for=URLPattern lt="URLPattern(input, options)">new URLPattern(|input|, |options|)</dfn> constructor steps are:
1. Run [=initialize=] given [=this=], |input|, null, and |options|.
</div>
<div algorithm>
To <dfn for=URLPattern>initialize</dfn> a {{URLPattern}} given a {{URLPattern}} |this|, {{URLPatternInput}} |input|, string or null |baseURL|, and {{URLPatternOptions}} |options|:
1. Set |this|'s [=URLPattern/associated URL pattern=] to the result of [=create=] given |input|, |baseURL|, and |options|.
</div>
<div algorithm>
The <dfn attribute for="URLPattern">protocol</dfn> getter steps are:
1. Return [=this=]'s [=URLPattern/associated URL pattern=]'s [=URL pattern/protocol component=]'s [=component/pattern string=].
</div>
<div algorithm>
The <dfn attribute for="URLPattern">username</dfn> getter steps are:
1. Return [=this=]'s [=URLPattern/associated URL pattern=]'s [=URL pattern/username component=]'s [=component/pattern string=].
</div>
<div algorithm>
The <dfn attribute for="URLPattern">password</dfn> getter steps are:
1. Return [=this=]'s [=URLPattern/associated URL pattern=]'s [=URL pattern/password component=]'s [=component/pattern string=].
</div>
<div algorithm>
The <dfn attribute for="URLPattern">hostname</dfn> getter steps are:
1. Return [=this=]'s [=URLPattern/associated URL pattern=]'s [=URL pattern/hostname component=]'s [=component/pattern string=].
</div>
<div algorithm>
The <dfn attribute for="URLPattern">port</dfn> getter steps are:
1. Return [=this=]'s [=URLPattern/associated URL pattern=]'s [=URL pattern/port component=]'s [=component/pattern string=].
</div>
<div algorithm>
The <dfn attribute for="URLPattern">pathname</dfn> getter steps are:
1. Return [=this=]'s [=URLPattern/associated URL pattern=]'s [=URL pattern/pathname component=]'s [=component/pattern string=].
</div>
<div algorithm>
The <dfn attribute for="URLPattern">search</dfn> getter steps are:
1. Return [=this=]'s [=URLPattern/associated URL pattern=]'s [=URL pattern/search component=]'s [=component/pattern string=].
</div>
<div algorithm>
The <dfn attribute for="URLPattern">hash</dfn> getter steps are:
1. Return [=this=]'s [=URLPattern/associated URL pattern=]'s [=URL pattern/hash component=]'s [=component/pattern string=].
</div>
<div algorithm>
The <dfn attribute for="URLPattern">hasRegExpGroups</dfn> getter steps are:
1. If [=this=]'s [=URLPattern/associated URL pattern=]'s [=URL pattern/has regexp groups=], then return true.
1. Return false.
</div>
<div algorithm>
The <dfn method for="URLPattern">test(|input|, |baseURL|)</dfn> method steps are:
1. Let |result| be the result of [=URL pattern/match=] given [=this=]'s [=URLPattern/associated URL pattern=], |input|, and |baseURL| if given.
1. If |result| is null, return false.
1. Return true.
</div>
<div algorithm>
The <dfn method for="URLPattern">exec(|input|, |baseURL|)</dfn> method steps are:
1. Return the result of [=URL pattern/match=] given [=this=]'s [=URLPattern/associated URL pattern=], |input|, and |baseURL| if given.
</div>
<h3 id=url-pattern-struct>The URL pattern struct</h3>
A <dfn export>URL pattern</dfn> is a [=struct=] with the following [=struct/items=]:
* <dfn for="URL pattern">protocol component</dfn>, a [=component=]
* <dfn for="URL pattern">username component</dfn>, a [=component=]
* <dfn for="URL pattern">password component</dfn>, a [=component=]
* <dfn for="URL pattern">hostname component</dfn>, a [=component=]
* <dfn for="URL pattern">port component</dfn>, a [=component=]
* <dfn for="URL pattern">pathname component</dfn>, a [=component=]
* <dfn for="URL pattern">search component</dfn>, a [=component=]
* <dfn for="URL pattern">hash component</dfn>, a [=component=]
A <dfn>component</dfn> is a [=struct=] with the following [=struct/items=]:
* <dfn for=component>pattern string</dfn>, a [=pattern string/well formed=] [=/pattern string=]
* <dfn for=component>regular expression</dfn>, a {{RegExp}}
* <dfn for=component>group name list</dfn>, a [=list=] of strings
* <dfn for=component>has regexp groups</dfn>, a [=boolean=]
<h3 id=high-level-operations>High-level operations</h3>
<div algorithm>
To <dfn export for="URL pattern">create</dfn> a [=URL pattern=] given a {{URLPatternInput}} |input|, string or null |baseURL|, and {{URLPatternOptions}} |options|:
1. Let |init| be null.
1. If |input| is a [=scalar value string=] then:
1. Set |init| to the result of running [=parse a constructor string=] given |input|.
1. If |baseURL| is null and |init|["{{URLPatternInit/protocol}}"] does not [=map/exist=], then throw a {{TypeError}}.
1. If |baseURL| is not null, [=map/set=] |init|["{{URLPatternInit/baseURL}}"] to |baseURL|.
1. Otherwise:
1. [=Assert=]: |input| is a {{URLPatternInit}}.
1. If |baseURL| is not null, then throw a {{TypeError}}.
1. Set |init| to |input|.
1. Let |processedInit| be the result of [=process a URLPatternInit=] given |init|, "`pattern`", null, null, null, null, null, null, null, and null.
1. [=list/For each=] |componentName| of « "{{URLPatternInit/protocol}}", "{{URLPatternInit/username}}", "{{URLPatternInit/password}}", "{{URLPatternInit/hostname}}", "{{URLPatternInit/port}}", "{{URLPatternInit/pathname}}", "{{URLPatternInit/search}}", "{{URLPatternInit/hash}}" »:
1. If |processedInit|[|componentName|] does not [=map/exist=], then [=map/set=] |processedInit|[|componentName|] to "`*`".
1. If |processedInit|["{{URLPatternInit/protocol}}"] is a [=special scheme=] and |processedInit|["{{URLPatternInit/port}}"] is a string which represents its corresponding [=default port=] in radix-10 using [=ASCII digits=] then set |processedInit|["{{URLPatternInit/port}}"] to the empty string.
1. Let |urlPattern| be a new [=URL pattern=].
1. Set |urlPattern|'s [=URL pattern/protocol component=] to the result of [=compiling a component=] given |processedInit|["{{URLPatternInit/protocol}}"], [=canonicalize a protocol=], and [=default options=].
1. Set |urlPattern|'s [=URL pattern/username component=] to the result of [=compiling a component=] given |processedInit|["{{URLPatternInit/username}}"], [=canonicalize a username=], and [=default options=].
1. Set |urlPattern|'s [=URL pattern/password component=] to the result of [=compiling a component=] given |processedInit|["{{URLPatternInit/password}}"], [=canonicalize a password=], and [=default options=].
1. If the result running [=hostname pattern is an IPv6 address=] given |processedInit|["{{URLPatternInit/hostname}}"] is true, then set |urlPattern|'s [=URL pattern/hostname component=] to the result of [=compiling a component=] given |processedInit|["{{URLPatternInit/hostname}}"], [=canonicalize an IPv6 hostname=], and [=hostname options=].
1. Otherwise, set |urlPattern|'s [=URL pattern/hostname component=] to the result of [=compiling a component=] given |processedInit|["{{URLPatternInit/hostname}}"], [=canonicalize a hostname=], and [=hostname options=].
1. Set |urlPattern|'s [=URL pattern/port component=] to the result of [=compiling a component=] given |processedInit|["{{URLPatternInit/port}}"], [=canonicalize a port=], and [=default options=].
1. Let |compileOptions| be a copy of the [=default options=] with the [=options/ignore case=] property set to |options|["{{URLPatternOptions/ignoreCase}}"].
1. If the result of running [=protocol component matches a special scheme=] given |urlPattern|'s [=URL pattern/protocol component=] is true, then:
1. Let |pathCompileOptions| be copy of the [=pathname options=] with the [=options/ignore case=] property set to |options|["{{URLPatternOptions/ignoreCase}}"].
1. Set |urlPattern|'s [=URL pattern/pathname component=] to the result of [=compiling a component=] given |processedInit|["{{URLPatternInit/pathname}}"], [=canonicalize a pathname=], and |pathCompileOptions|.
1. Otherwise set |urlPattern|'s [=URL pattern/pathname component=] to the result of [=compiling a component=] given |processedInit|["{{URLPatternInit/pathname}}"], [=canonicalize an opaque pathname=], and |compileOptions|.
1. Set |urlPattern|'s [=URL pattern/search component=] to the result of [=compiling a component=] given |processedInit|["{{URLPatternInit/search}}"], [=canonicalize a search=], and |compileOptions|.
1. Set |urlPattern|'s [=URL pattern/hash component=] to the result of [=compiling a component=] given |processedInit|["{{URLPatternInit/hash}}"], [=canonicalize a hash=], and |compileOptions|.
1. Return |urlPattern|.
</div>
<div algorithm>
To perform a <dfn export for="URL pattern">match</dfn> given a [=URL pattern=] |urlPattern|, a {{URLPatternInput}} or [=/URL=] |input|, and an optional string |baseURLString|:
1. Let |protocol| be the empty string.
1. Let |username| be the empty string.
1. Let |password| be the empty string.
1. Let |hostname| be the empty string.
1. Let |port| be the empty string.
1. Let |pathname| be the empty string.
1. Let |search| be the empty string.
1. Let |hash| be the empty string.
1. Let |inputs| be an empty [=list=].
1. [=list/Append=] |input| to |inputs|.
1. If |input| is a {{URLPatternInit}} then:
1. If |baseURLString| was given, throw a {{TypeError}}.
1. Let |applyResult| be the result of [=process a URLPatternInit=] given |input|, "url", |protocol|, |username|, |password|, |hostname|, |port|, |pathname|, |search|, and |hash|. If this throws an exception, catch it, and return null.
1. Set |protocol| to |applyResult|["{{URLPatternInit/protocol}}"].
1. Set |username| to |applyResult|["{{URLPatternInit/username}}"].
1. Set |password| to |applyResult|["{{URLPatternInit/password}}"].
1. Set |hostname| to |applyResult|["{{URLPatternInit/hostname}}"].
1. Set |port| to |applyResult|["{{URLPatternInit/port}}"].
1. Set |pathname| to |applyResult|["{{URLPatternInit/pathname}}"].
1. Set |search| to |applyResult|["{{URLPatternInit/search}}"].
1. Set |hash| to |applyResult|["{{URLPatternInit/hash}}"].
1. Otherwise:
1. Let |url| be |input|.
1. If |input| is a {{USVString}}:
1. Let |baseURL| be null.
1. If |baseURLString| was given, then:
1. Set |baseURL| to the result of running the [=basic URL parser=] on |baseURLString|.
1. If |baseURL| is failure, return null.
1. [=list/Append=] |baseURLString| to |inputs|.
1. Set |url| to the result of running the [=basic URL parser=] on |input| with |baseURL|.
1. If |url| is failure, return null.
1. [=Assert=]: |url| is a [=/URL=].
1. Set |protocol| to |url|'s [=url/scheme=].
1. Set |username| to |url|'s [=url/username=].
1. Set |password| to |url|'s [=url/password=].
1. Set |hostname| to |url|'s [=url/host=], [=host serializer|serialized=], or the empty string if the value is null.
1. Set |port| to |url|'s [=url/port=], [=serialize an integer|serialized=], or the empty string if the value is null.
1. Set |pathname| to the result of [=URL path serializing=] |url|.
1. Set |search| to |url|'s [=url/query=] or the empty string if the value is null.
1. Set |hash| to |url|'s [=url/fragment=] or the empty string if the value is null.
1. Let |protocolExecResult| be [$RegExpBuiltinExec$](|urlPattern|'s [=URL pattern/protocol component=]'s [=component/regular expression=], |protocol|).
1. Let |usernameExecResult| be [$RegExpBuiltinExec$](|urlPattern|'s [=URL pattern/username component=]'s [=component/regular expression=], |username|).
1. Let |passwordExecResult| be [$RegExpBuiltinExec$](|urlPattern|'s [=URL pattern/password component=]'s [=component/regular expression=], |password|).
1. Let |hostnameExecResult| be [$RegExpBuiltinExec$](|urlPattern|'s [=URL pattern/hostname component=]'s [=component/regular expression=], |hostname|).
1. Let |portExecResult| be [$RegExpBuiltinExec$](|urlPattern|'s [=URL pattern/port component=]'s [=component/regular expression=], |port|).
1. Let |pathnameExecResult| be [$RegExpBuiltinExec$](|urlPattern|'s [=URL pattern/pathname component=]'s [=component/regular expression=], |pathname|).
1. Let |searchExecResult| be [$RegExpBuiltinExec$](|urlPattern|'s [=URL pattern/search component=]'s [=component/regular expression=], |search|).
1. Let |hashExecResult| be [$RegExpBuiltinExec$](|urlPattern|'s [=URL pattern/hash component=]'s [=component/regular expression=], |hash|).
1. If |protocolExecResult|, |usernameExecResult|, |passwordExecResult|, |hostnameExecResult|, |portExecResult|, |pathnameExecResult|, |searchExecResult|, or |hashExecResult| are null then return null.
1. Let |result| be a new {{URLPatternResult}}.
1. Set |result|["{{URLPatternResult/inputs}}"] to |inputs|.
1. Set |result|["{{URLPatternResult/protocol}}"] to the result of [=creating a component match result=] given |urlPattern|'s [=URL pattern/protocol component=], |protocol|, and |protocolExecResult|.
1. Set |result|["{{URLPatternResult/username}}"] to the result of [=creating a component match result=] given |urlPattern|'s [=URL pattern/username component=], |username|, and |usernameExecResult|.
1. Set |result|["{{URLPatternResult/password}}"] to the result of [=creating a component match result=] given |urlPattern|'s [=URL pattern/password component=], |password|, and |passwordExecResult|.
1. Set |result|["{{URLPatternResult/hostname}}"] to the result of [=creating a component match result=] given |urlPattern|'s [=URL pattern/hostname component=], |hostname|, and |hostnameExecResult|.
1. Set |result|["{{URLPatternResult/port}}"] to the result of [=creating a component match result=] given |urlPattern|'s [=URL pattern/port component=], |port|, and |portExecResult|.
1. Set |result|["{{URLPatternResult/pathname}}"] to the result of [=creating a component match result=] given |urlPattern|'s [=URL pattern/pathname component=], |pathname|, and |pathnameExecResult|.
1. Set |result|["{{URLPatternResult/search}}"] to the result of [=creating a component match result=] given |urlPattern|'s [=URL pattern/search component=], |search|, and |searchExecResult|.
1. Set |result|["{{URLPatternResult/hash}}"] to the result of [=creating a component match result=] given |urlPattern|'s [=URL pattern/hash component=], |hash|, and |hashExecResult|.
1. Return |result|.
</div>
<div algorithm>
A [=URL pattern=] |urlPattern| <dfn export for="URL pattern">has regexp groups</dfn> if the following steps return true:
1. If |urlPattern|'s [=URL pattern/protocol component=] [=component/has regexp groups=] is true, then return true.
1. If |urlPattern|'s [=URL pattern/username component=] [=component/has regexp groups=] is true, then return true.
1. If |urlPattern|'s [=URL pattern/password component=] [=component/has regexp groups=] is true, then return true.
1. If |urlPattern|'s [=URL pattern/hostname component=] [=component/has regexp groups=] is true, then return true.
1. If |urlPattern|'s [=URL pattern/port component=] [=component/has regexp groups=] is true, then return true.
1. If |urlPattern|'s [=URL pattern/pathname component=] [=component/has regexp groups=] is true, then return true.
1. If |urlPattern|'s [=URL pattern/search component=] [=component/has regexp groups=] is true, then return true.
1. If |urlPattern|'s [=URL pattern/hash component=] [=component/has regexp groups=] is true, then return true.
1. Return false.
</div>
<h3 id=urlpattern-internals>Internals</h3>
<div algorithm>
To <dfn>compile a component</dfn> given a string |input|, [=/encoding callback=] |encoding callback|, and [=/options=] |options|:
1. Let |part list| be the result of running [=parse a pattern string=] given |input|, |options|, and |encoding callback|.
1. Let (|regular expression string|, |name list|) be the result of running [=generate a regular expression and name list=] given |part list| and |options|.
1. Let |flags| be an empty string.
1. If |options|'s [=options/ignore case=] is true then set |flags| to "`vi`".
1. Otherwise set |flags| to "`v`"
1. Let |regular expression| be [$RegExpCreate$](|regular expression string|, |flags|). If this throws an exception, catch it, and throw a {{TypeError}}.
<p class="note">The specification uses regular expressions to perform all matching, but this is not mandated. Implementations are free to perform matching directly against the [=/part list=] when possible; e.g. when there are no custom regexp matching groups. If there are custom regular expressions, however, its important that they be immediately evaluated in the [=compile a component=] algorithm so an error can be thrown if they are invalid.
1. Let |pattern string| be the result of running [=generate a pattern string=] given |part list| and |options|.
1. Let |has regexp groups| be false.
1. [=list/For each=] |part| of |part list|:
1. If |part|'s [=part/type=] is "<a for=part/type>`regexp`</a>", then set |has regexp groups| to true.
1. Return a new [=component=] whose [=component/pattern string=] is |pattern string|, [=component/regular expression=] is |regular expression|, [=component/group name list=] is |name list|, and [=component/has regexp groups=] is |has regexp groups|.
</div>
<div algorithm>
To <dfn>create a component match result</dfn> given a [=component=] |component|, a string |input|, and an array representing the output of [$RegExpBuiltinExec$] |execResult|:
1. Let |result| be a new {{URLPatternComponentResult}}.
1. Set |result|["{{URLPatternComponentResult/input}}"] to |input|.
1. Let |groups| be a <code>[=record=]<{{USVString}}, ({{USVString}} or {{undefined}})></code>.
1. Let |index| be 1.
1. While |index| is less than [$Get$](|execResult|, "`length`"):
1. Let |name| be |component|'s [=component/group name list=][|index| − 1].
1. Let |value| be [$Get$](|execResult|, [$ToString$](|index|)).
1. Set |groups|[|name|] to |value|.
1. Increment |index| by 1.
1. Set |result|["{{URLPatternComponentResult/groups}}"] to |groups|.
1. Return |result|.
</div>
The <dfn>default options</dfn> is an [=options=] [=struct=] with [=options/delimiter code point=] set to the empty string and [=options/prefix code point=] set to the empty string.
The <dfn>hostname options</dfn> is an [=options=] [=struct=] with [=options/delimiter code point=] set "`.`" and [=options/prefix code point=] set to the empty string.
The <dfn>pathname options</dfn> is an [=options=] [=struct=] with [=options/delimiter code point=] set "`/`" and [=options/prefix code point=] set to "`/`".
<div algorithm>
To determine if a <dfn>protocol component matches a special scheme</dfn> given a [=component=] |protocol component|:
1. Let |special scheme list| be a [=list=] populated with all of the [=special schemes=].
1. [=list/For each=] |scheme| of |special scheme list|:
1. Let |test result| be [$RegExpBuiltinExec$](|protocol component|'s [=component/regular expression=], |scheme|).
1. If |test result| is not null, then return true.
1. Return false.
</div>
<div algorithm>
To determine if a <dfn>hostname pattern is an IPv6 address</dfn> given a [=/pattern string=] |input|:
1. If |input|'s [=string/code point length=] is less than 2, then return false.
1. Let |input code points| be |input| interpreted as a [=list=] of [=/code points=].
1. If |input code points|[0] is U+005B (`[`), then return true.
1. If |input code points|[0] is U+007B (`{`) and |input code points|[1] is U+005B (`[`), then return true.
1. If |input code points|[0] is U+005C (<code>\</code>) and |input code points|[1] is U+005B (`[`), then return true.
1. Return false.
</div>
<h3 id=constructor-string-parsing>Constructor string parsing</h3>
A <dfn export>constructor string parser</dfn> is a [=struct=].
A [=constructor string parser=] has an associated <dfn export for="constructor string parser">input</dfn>, a string, which must be set upon creation.
A [=constructor string parser=] has an associated <dfn export for="constructor string parser">token list</dfn>, a [=/token list=], which must be set upon creation.
A [=constructor string parser=] has an associated <dfn export for="constructor string parser">result</dfn>, a {{URLPatternInit}}, initially set to a new {{URLPatternInit}}.
A [=constructor string parser=] has an associated <dfn export for="constructor string parser">component start</dfn>, a number, initially set to 0.
A [=constructor string parser=] has an associated <dfn export for="constructor string parser">token index</dfn>, a number, initially set to 0.
A [=constructor string parser=] has an associated <dfn export for="constructor string parser">token increment</dfn>, a number, initially set to 1.
A [=constructor string parser=] has an associated <dfn export for="constructor string parser">group depth</dfn>, a number, initially set to 0.
A [=constructor string parser=] has an associated <dfn export for="constructor string parser">hostname IPv6 bracket depth</dfn>, a number, initially set to 0.
A [=constructor string parser=] has an associated <dfn export for="constructor string parser">protocol matches a special scheme flag</dfn>, a boolean, initially set to false.
A [=constructor string parser=] has an associated <dfn export for="constructor string parser">state</dfn>, a string, initially set to "<a for="constructor string parser/state">`init`</a>". It must be one of the following:
<ul>
<li>"<dfn for="constructor string parser/state">`init`</dfn>"</li>
<li>"<dfn export for="constructor string parser/state">`protocol`</dfn>"</li>
<li>"<dfn export for="constructor string parser/state">`authority`</dfn>"</li>
<li>"<dfn export for="constructor string parser/state">`username`</dfn>"</li>
<li>"<dfn export for="constructor string parser/state">`password`</dfn>"</li>
<li>"<dfn export for="constructor string parser/state">`hostname`</dfn>"</li>
<li>"<dfn export for="constructor string parser/state">`port`</dfn>"</li>
<li>"<dfn export for="constructor string parser/state">`pathname`</dfn>"</li>
<li>"<dfn export for="constructor string parser/state">`search`</dfn>"</li>
<li>"<dfn export for="constructor string parser/state">`hash`</dfn>"</li>
<li>"<dfn export for="constructor string parser/state">`done`</dfn>"</li>
</ul>
<div class=note>
<p>The URLPattern constructor string algorithm is very similar to the [=basic URL parser=] algorithm, but some differences prevent us from using that algorithm directly.
<p>First, the URLPattern constructor string parser operates on [=tokens=] generated using the "`lenient`" [=tokenize policy=]. In constrast, [=basic URL parser=] operates on code points. Operating on [=tokens=] allows the URLPattern constructor string parser to more easily distinguish between code points that are significant pattern syntax and code points that might be a URL component separator. For example, it makes it trivial to handle named groups like "`:hmm`" in "`https://a.c:hmm.example.com:8080`" without getting confused with the port number.
<p>Second, the URLPattern constructor string parser needs to avoid applying URL canonicalization to all code points like [=basic URL parser=] does. Instead we perform canonicalization on only parts of the pattern string we know are safe later when compiling each component pattern string.
<p>Finally, the URLPattern constructor string parser does not handle some parts of the [=basic URL parser=] state machine. For example, it does not treat backslashes specially as they would all be treated as pattern characters and would require excessive escaping. In addition, this parser might not handle some more esoteric parts of the URL parsing algorithm like file URLs with a hostname. The goal with this parser was to handle the most common URLs while allowing any niche case to be handled instead via the {{URLPatternInit}} constructor.
</div>
<div class=note>
<p>In the constructor string algorithm, the pathname, search, and hash are wildcarded if earlier components are specified but later ones are not. For example, "`https://example.com/foo`" matches any search and any hash. Similarly, "`https://example.com`" matches any URL on that origin. This is analogous to the notion of a more specific component in the notes about [=process a URLPatternInit=] (e.g., a search is more specific than a pathname), but the constructor syntax only has a few cases where it is possible to specify a more specific component without also specifying the less specific components.
<p>The username and password components are always wildcard unless they are explicitly specified.
<p>If a hostname is specified and the port is not, the port is assumed to be the default port. If authors want to match any port, they have to write `:*` explicitly. For example, "`https://*`" is any HTTPS origin on port 443, and "`https://*:*`" is any HTTPS origin on any port.
</div>
<div algorithm>
To <dfn>parse a constructor string</dfn> given a string |input|:
1. Let |parser| be a new [=constructor string parser=] whose [=constructor string parser/input=] is |input| and [=constructor string parser/token list=] is the result of running [=tokenize=] given |input| and "<a for="tokenize policy">`lenient`</a>".
1. [=While=] |parser|'s [=constructor string parser/token index=] is less than |parser|'s [=constructor string parser/token list=] [=list/size=]:
1. Set |parser|'s [=constructor string parser/token increment=] to 1.
<p class="note">On every iteration of the parse loop the |parser|'s [=constructor string parser/token index=] will be incremented by its [=constructor string parser/token increment=] value. Typically this means incrementing by 1, but at certain times it is set to zero. The [=constructor string parser/token increment=] is then always reset back to 1 at the top of the loop.
1. If |parser|'s [=constructor string parser/token list=][|parser|'s [=constructor string parser/token index=]]'s [=token/type=] is "<a for=token/type>`end`</a>" then:
1. If |parser|'s [=constructor string parser/state=] is "<a for="constructor string parser/state">`init`</a>":
<p class="note">If we reached the end of the string in the "<a for="constructor string parser/state">`init`</a>" [=constructor string parser/state=], then we failed to find a protocol terminator and this has to be a relative URLPattern constructor string.
1. Run [=rewind=] given |parser|.
<p class=note>We next determine at which component the relative pattern begins. Relative pathnames are most common, but URLs and URLPattern constructor strings can begin with the search or hash components as well.
1. If the result of running [=is a hash prefix=] given |parser| is true, then run [=change state=] given |parser|, "<a for="constructor string parser/state">`hash`</a>" and 1.
1. Otherwise if the result of running [=is a search prefix=] given |parser| is true:
1. Run [=change state=] given |parser|, "<a for="constructor string parser/state">`search`</a>" and 1.
1. Otherwise:
1. Run [=change state=] given |parser|, "<a for="constructor string parser/state">`pathname`</a>" and 0.
1. Increment |parser|'s [=constructor string parser/token index=] by |parser|'s [=constructor string parser/token increment=].
1. [=Continue=].
1. If |parser|'s [=constructor string parser/state=] is "<a for="constructor string parser/state">`authority`</a>":
<p class=note>If we reached the end of the string in the "<a for="constructor string parser/state">`authority`</a>" [=constructor string parser/state=], then we failed to find an "`@`". Therefore there is no username or password.
1. Run [=rewind and set state=] given |parser|, and "<a for="constructor string parser/state">`hostname`</a>".
1. Increment |parser|'s [=constructor string parser/token index=] by |parser|'s [=constructor string parser/token increment=].
1. [=Continue=].
1. Run [=change state=] given |parser|, "<a for="constructor string parser/state">`done`</a>" and 0.
1. [=Break=].
1. If the result of running [=is a group open=] given |parser| is true:
<div class=note>
<p>We ignore all code points within "`{ ... }`" pattern groupings. It would not make sense to allow a URL component boundary to lie within a grouping; e.g. "`https://example.c{om/fo}o`". While not supported within [=well formed=] [=/pattern strings=], we handle nested groupings here to avoid parser confusion.
<p>It is not necessary to perform this logic for regexp or named groups since those values are collapsed into individual [=tokens=] by the [=tokenize=] algorithm.
</div>
1. Increment |parser|'s [=constructor string parser/group depth=] by 1.
1. Increment |parser|'s [=constructor string parser/token index=] by |parser|'s [=constructor string parser/token increment=].
1. [=Continue=].
1. If |parser|'s [=constructor string parser/group depth=] is greater than 0:
1. If the result of running [=is a group close=] given |parser| is true, then decrement |parser|'s [=constructor string parser/group depth=] by 1.
1. Otherwise:
1. Increment |parser|'s [=constructor string parser/token index=] by |parser|'s [=constructor string parser/token increment=].
1. [=Continue=].
1. Switch on |parser|'s [=constructor string parser/state=] and run the associated steps:
<dl class="switch">
<dt>"<a for="constructor string parser/state">`init`</a>"</dt>
<dd>
1. If the result of running [=is a protocol suffix=] given |parser| is true:
1. Run [=rewind and set state=] given |parser| and "<a for="constructor string parser/state">`protocol`</a>".
</dd>
<dt>"<a for="constructor string parser/state">`protocol`</a>"</dt>
<dd>
1. If the result of running [=is a protocol suffix=] given |parser| is true:
1. Run [=compute protocol matches a special scheme flag=] given |parser|.
<p class="note">We need to eagerly compile the protocol component to determine if it matches any [=special schemes=]. If it does then certain special rules apply. It determines if the pathname defaults to a "`/`" and also whether we will look for the username, password, hostname, and port components. Authority slashes can also cause us to look for these components as well. Otherwise we treat this as an "opaque path URL" and go straight to the pathname component.
1. Let |next state| be "<a for="constructor string parser/state">`pathname`</a>".
1. Let |skip| be 1.
1. If the result of running [=next is authority slashes=] given |parser| is true:
1. Set |next state| to "<a for="constructor string parser/state">`authority`</a>".
1. Set |skip| to 3.
1. Otherwise if |parser|'s [=constructor string parser/protocol matches a special scheme flag=] is true, then set |next state| to "<a for="constructor string parser/state">`authority`</a>".
1. Run [=change state=] given |parser|, |next state|, and |skip|.
</dd>
<dt>"<a for="constructor string parser/state">`authority`</a>"</dt>
<dd>
1. If the result of running [=is an identity terminator=] given |parser| is true, then run [=rewind and set state=] given |parser| and "<a for="constructor string parser/state">`username`</a>".
1. Otherwise if any of the following are true:
<ul>
<li>the result of running [=is a pathname start=] given |parser|;</li>
<li>the result of running [=is a search prefix=] given |parser|; or</li>
<li>the result of running [=is a hash prefix=] given |parser|,</li>
</ul>
<p>then run [=rewind and set state=] given |parser| and "<a for="constructor string parser/state">`hostname`</a>".
</dd>
<dt>"<a for="constructor string parser/state">`username`</a>"</dt>
<dd>
1. If the result of running [=is a password prefix=] given |parser| is true, then run [=change state=] given |parser|, "<a for="constructor string parser/state">`password`</a>", and 1.
1. Otherwise if the result of running [=is an identity terminator=] given |parser| is true, then run [=change state=] given |parser|, "<a for="constructor string parser/state">`hostname`</a>", and 1.
</dd>
<dt>"<a for="constructor string parser/state">`password`</a>"</dt>
<dd>
1. If the result of running [=is an identity terminator=] given |parser| is true, then run [=change state=] given |parser|, "<a for="constructor string parser/state">`hostname`</a>", and 1.
</dd>
<dt>"<a for="constructor string parser/state">`hostname`</a>"</dt>
<dd>
1. If the result of running [=is an IPv6 open=] given |parser| is true, then increment |parser|'s [=constructor string parser/hostname IPv6 bracket depth=] by 1.
1. Otherwise if the result of running [=is an IPv6 close=] given |parser| is true, then decrement |parser|'s [=constructor string parser/hostname IPv6 bracket depth=] by 1.
1. Otherwise if the result of running [=is a port prefix=] given |parser| is true and |parser|'s [=constructor string parser/hostname IPv6 bracket depth=] is zero, then run [=change state=] given |parser|, "<a for="constructor string parser/state">`port`</a>", and 1.
1. Otherwise if the result of running [=is a pathname start=] given |parser| is true, then run [=change state=] given |parser|, "<a for="constructor string parser/state">`pathname`</a>", and 0.
1. Otherwise if the result of running [=is a search prefix=] given |parser| is true, then run [=change state=] given |parser|, "<a for="constructor string parser/state">`search`</a>", and 1.
1. Otherwise if the result of running [=is a hash prefix=] given |parser| is true, then run [=change state=] given |parser|, "<a for="constructor string parser/state">`hash`</a>", and 1.
</dd>
<dt>"<a for="constructor string parser/state">`port`</a>"</dt>
<dd>
1. If the result of running [=is a pathname start=] given |parser| is true, then run [=change state=] given |parser|, "<a for="constructor string parser/state">`pathname`</a>", and 0.
1. Otherwise if the result of running [=is a search prefix=] given |parser| is true, then run [=change state=] given |parser|, "<a for="constructor string parser/state">`search`</a>", and 1.
1. Otherwise if the result of running [=is a hash prefix=] given |parser| is true, then run [=change state=] given |parser|, "<a for="constructor string parser/state">`hash`</a>", and 1.
</dd>
<dt>"<a for="constructor string parser/state">`pathname`</a>"</dt>
<dd>
1. If the result of running [=is a search prefix=] given |parser| is true, then run [=change state=] given |parser|, "<a for="constructor string parser/state">`search`</a>", and 1.
1. Otherwise if the result of running [=is a hash prefix=] given |parser| is true, then run [=change state=] given |parser|, "<a for="constructor string parser/state">`hash`</a>", and 1.
</dd>
<dt>"<a for="constructor string parser/state">`search`</a>"</dt>
<dd>
1. If the result of running [=is a hash prefix=] given |parser| is true, then run [=change state=] given |parser|, "<a for="constructor string parser/state">`hash`</a>", and 1.
</dd>
<dt>"<a for="constructor string parser/state">`hash`</a>"</dt>
<dd>
1. Do nothing.
</dd>
<dt>"<a for="constructor string parser/state">`done`</a>"</dt>
<dd>
1. [=Assert=]: This step is never reached.
</dd>
</dl>
1. Increment |parser|'s [=constructor string parser/token index=] by |parser|'s [=constructor string parser/token increment=].
1. If |parser|'s [=constructor string parser/result=] [=map/contains=] "{{URLPatternInit/hostname}}" and not "{{URLPatternInit/port}}", then set |parser|'s [=constructor string parser/result=]["{{URLPatternInit/port}}"] to the empty string.
<div class="note">This is special-cased because when an author does not specify a port, they usually intend the default port. If any port is acceptable, the author can specify it as a wildcard explicitly. For example, "`https://example.com/*`" does not match URLs beginning with "`https://example.com:8443/`", which is a different origin.</div>
1. Return |parser|'s [=constructor string parser/result=].
</div>
<div algorithm>
To <dfn>change state</dfn> given a [=constructor string parser=] |parser|, a [=constructor string parser/state=] |new state|, and a number |skip|:
1. If |parser|'s [=constructor string parser/state=] is not "<a for="constructor string parser/state">`init`</a>", not "<a for="constructor string parser/state">`authority`</a>", and not "<a for="constructor string parser/state">`done`</a>", then set |parser|'s [=constructor string parser/result=][|parser|'s [=constructor string parser/state=]] to the result of running [=make a component string=] given |parser|.
1. If |parser|'s [=constructor string parser/state=] is not "<a for="constructor string parser/state">`init`</a>" and |new state| is not "<a for="constructor string parser/state">`done`</a>", then:
1. If |parser|'s [=constructor string parser/state=] is "<a for="constructor string parser/state">`protocol`</a>", "<a for="constructor string parser/state">`authority`</a>", "<a for="constructor string parser/state">`username`</a>", or "<a for="constructor string parser/state">`password`</a>"; |new state| is "<a for="constructor string parser/state">`port`</a>", "<a for="constructor string parser/state">`pathname`</a>", "<a for="constructor string parser/state">`search`</a>", or "<a for="constructor string parser/state">`hash`</a>"; and |parser|'s [=constructor string parser/result=]["{{URLPatternInit/hostname}}"] does not [=map/exist=], then set |parser|'s [=constructor string parser/result=]["{{URLPatternInit/hostname}}"] to the empty string.
1. If |parser|'s [=constructor string parser/state=] is "<a for="constructor string parser/state">`protocol`</a>", "<a for="constructor string parser/state">`authority`</a>", "<a for="constructor string parser/state">`username`</a>", "<a for="constructor string parser/state">`password`</a>", "<a for="constructor string parser/state">`hostname`</a>", or "<a for="constructor string parser/state">`port`</a>"; |new state| is "<a for="constructor string parser/state">`search`</a>" or "<a for="constructor string parser/state">`hash`</a>"; and |parser|'s [=constructor string parser/result=]["{{URLPatternInit/pathname}}"] does not [=map/exist=], then:
1. If |parser|'s [=constructor string parser/protocol matches a special scheme flag=] is true, then set |parser|'s [=constructor string parser/result=]["{{URLPatternInit/pathname}}"] to "`/`".
1. Otherwise, set |parser|'s [=constructor string parser/result=]["{{URLPatternInit/pathname}}"] to the empty string.
1. If |parser|'s [=constructor string parser/state=] is "<a for="constructor string parser/state">`protocol`</a>", "<a for="constructor string parser/state">`authority`</a>", "<a for="constructor string parser/state">`username`</a>", "<a for="constructor string parser/state">`password`</a>", "<a for="constructor string parser/state">`hostname`</a>", "<a for="constructor string parser/state">`port`</a>", or "<a for="constructor string parser/state">`pathname`</a>"; |new state| is "<a for="constructor string parser/state">`hash`</a>"; and |parser|'s [=constructor string parser/result=]["{{URLPatternInit/search}}"] does not [=map/exist=], then set |parser|'s [=constructor string parser/result=]["{{URLPatternInit/search}}"] to the empty string.
1. Set |parser|'s [=constructor string parser/state=] to |new state|.
1. Increment |parser|'s [=constructor string parser/token index=] by |skip|.
1. Set |parser|'s [=constructor string parser/component start=] to |parser|'s [=constructor string parser/token index=].
1. Set |parser|'s [=constructor string parser/token increment=] to 0.
</div>
<div algorithm>
To <dfn>rewind</dfn> given a [=constructor string parser=] |parser|:
1. Set |parser|'s [=constructor string parser/token index=] to |parser|'s [=constructor string parser/component start=].
1. Set |parser|'s [=constructor string parser/token increment=] to 0.
</div>
<div algorithm>
To <dfn>rewind and set state</dfn> given a [=constructor string parser=] |parser| and a [=constructor string parser/state=] |state|:
1. Run [=rewind=] given |parser|.
1. Set |parser|'s [=constructor string parser/state=] to |state|.
</div>
<div algorithm>
To <dfn>get a safe token</dfn> given a [=constructor string parser=] |parser| and a number |index|:
1. If |index| is less than |parser|'s [=constructor string parser/token list=]'s [=list/size=], then return |parser|'s [=constructor string parser/token list=][|index|].
1. [=Assert=]: |parser|'s [=constructor string parser/token list=]'s [=list/size=] is greater than or equal to 1.
1. Let |last index| be |parser|'s [=constructor string parser/token list=]'s [=list/size=] − 1.
1. Let |token| be |parser|'s [=constructor string parser/token list=][|last index|].
1. [=Assert=]: |token|'s [=token/type=] is "<a for=token/type>`end`</a>".
1. Return |token|.
</div>
<div algorithm>
To run <dfn>is a non-special pattern char</dfn> given a [=constructor string parser=] |parser|, a number |index|, and a string |value|:
1. Let |token| be the result of running [=get a safe token=] given |parser| and |index|.
1. If |token|'s [=token/value=] is not |value|, then return false.
1. If any of the following are true:
<ul>
<li>|token|'s [=token/type=] is "<a for=token/type>`char`</a>";
<li>|token|'s [=token/type=] is "<a for=token/type>`escaped-char`</a>"; or
<li>|token|'s [=token/type=] is "<a for=token/type>`invalid-char`</a>",
</ul>
<p>then return true.
1. Return false.
</div>
<div algorithm>
To run <dfn>is a protocol suffix</dfn> given a [=constructor string parser=] |parser|:
1. Return the result of running [=is a non-special pattern char=] given |parser|, |parser|'s [=constructor string parser/token index=], and "`:`".
</div>
<div algorithm>
To run <dfn>next is authority slashes</dfn> given a [=constructor string parser=] |parser|:
1. If the result of running [=is a non-special pattern char=] given |parser|, |parser|'s [=constructor string parser/token index=] + 1, and "`/`" is false, then return false.
1. If the result of running [=is a non-special pattern char=] given |parser|, |parser|'s [=constructor string parser/token index=] + 2, and "`/`" is false, then return false.
1. Return true.
</div>
<div algorithm>
To run <dfn>is an identity terminator</dfn> given a [=constructor string parser=] |parser|:
1. Return the result of running [=is a non-special pattern char=] given |parser|, |parser|'s [=constructor string parser/token index=], and "`@`".
</div>
<div algorithm>
To run <dfn>is a password prefix</dfn> given a [=constructor string parser=] |parser|:
1. Return the result of running [=is a non-special pattern char=] given |parser|, |parser|'s [=constructor string parser/token index=], and "`:`".
</div>
<div algorithm>
To run <dfn>is a port prefix</dfn> given a [=constructor string parser=] |parser|:
1. Return the result of running [=is a non-special pattern char=] given |parser|, |parser|'s [=constructor string parser/token index=], and "`:`".
</div>
<div algorithm>
To run <dfn>is a pathname start</dfn> given a [=constructor string parser=] |parser|:
1. Return the result of running [=is a non-special pattern char=] given |parser|, |parser|'s [=constructor string parser/token index=], and "`/`".
</div>
<div algorithm>
To run <dfn>is a search prefix</dfn> given a [=constructor string parser=] |parser|:
1. If result of running [=is a non-special pattern char=] given |parser|, |parser|'s [=constructor string parser/token index=] and "`?`" is true, then return true.
1. If |parser|'s [=constructor string parser/token list=][|parser|'s [=constructor string parser/token index=]]'s [=token/value=] is not "`?`", then return false.
1. Let |previous index| be |parser|'s [=constructor string parser/token index=] − 1.
1. If |previous index| is less than 0, then return true.
1. Let |previous token| be the result of running [=get a safe token=] given |parser| and |previous index|.
1. If any of the following are true, then return false:
<ul>
<li>|previous token|'s [=token/type=] is "<a for=token/type>`name`</a>".</li>
<li>|previous token|'s [=token/type=] is "<a for=token/type>`regexp`</a>".</li>
<li>|previous token|'s [=token/type=] is "<a for=token/type>`close`</a>".</li>
<li>|previous token|'s [=token/type=] is "<a for=token/type>`asterisk`</a>".</li>
</ul>
1. Return true.
</div>
<div algorithm>
To run <dfn>is a hash prefix</dfn> given a [=constructor string parser=] |parser|:
1. Return the result of running [=is a non-special pattern char=] given |parser|, |parser|'s [=constructor string parser/token index=] and "`#`".
</div>
<div algorithm>
To run <dfn>is a group open</dfn> given a [=constructor string parser=] |parser|:
1. If |parser|'s [=constructor string parser/token list=][|parser|'s [=constructor string parser/token index=]]'s [=token/type=] is "<a for=token/type>`open`</a>", then return true.
1. Otherwise return false.
</div>
<div algorithm>
To run <dfn>is a group close</dfn> given a [=constructor string parser=] |parser|:
1. If |parser|'s [=constructor string parser/token list=][|parser|'s [=constructor string parser/token index=]]'s [=token/type=] is "<a for=token/type>`close`</a>", then return true.
1. Otherwise return false.
</div>
<div algorithm>
To run <dfn>is an IPv6 open</dfn> given a [=constructor string parser=] |parser|:
1. Return the result of running [=is a non-special pattern char=] given |parser|, |parser|'s [=constructor string parser/token index=], and "`[`".
</div>
<div algorithm>
To run <dfn>is an IPv6 close</dfn> given a [=constructor string parser=] |parser|:
1. Return the result of running [=is a non-special pattern char=] given |parser|, |parser|'s [=constructor string parser/token index=], and "`]`".
</div>
<div algorithm>
To run <dfn>make a component string</dfn> given a [=constructor string parser=] |parser|:
1. [=Assert=]: |parser|'s [=constructor string parser/token index=] is less than |parser|'s [=constructor string parser/token list=]'s [=list/size=].
1. Let |token| be |parser|'s [=constructor string parser/token list=][|parser|'s [=constructor string parser/token index=]].
1. Let |component start token| be the result of running [=get a safe token=] given |parser| and |parser|'s [=constructor string parser/component start=].
1. Let |component start input index| be |component start token|'s [=token/index=].
1. Let |end index| be |token|'s [=token/index=].
1. Return the [=code point substring by positions|code point substring=] from |component start input index| to |end index| within |parser|'s [=constructor string parser/input=].
</div>
<div algorithm>
To <dfn>compute protocol matches a special scheme flag</dfn> given a [=constructor string parser=] |parser|:
1. Let |protocol string| be the result of running [=make a component string=] given |parser|.
1. Let |protocol component| be the result of [=compiling a component=] given |protocol string|, [=canonicalize a protocol=], and [=default options=].
1. If the result of running [=protocol component matches a special scheme=] given |protocol component| is true, then set |parser|'s [=constructor string parser/protocol matches a special scheme flag=] to true.
</div>
<h2 id=pattern-strings>Pattern strings</h2>
A <dfn>pattern string</dfn> is a string that is written to match a set of target strings. A <dfn for="pattern string">well formed</dfn> pattern string conforms to a particular pattern syntax. This pattern syntax is directly based on the syntax used by the popular [path-to-regexp](https://github.com/pillarjs/path-to-regexp) JavaScript library.
It can be [=parse a pattern string|parsed=] to produce a [=/part list=] which describes, in order, what must appear in a component string for the pattern string to match.
<div class="example" id="example-pattern-strings">
Pattern strings can contain capture groups, which by default match the shortest possible string, up to a component-specific separator (`/` in the pathname, `.` in the hostname). For example, the pathname pattern "`/blog/:title`" will match "`/blog/hello-world`" but not "`/blog/2012/02`".
A regular expression enclosed in parentheses can also be used instead, so the pathname pattern "`/blog/:year(\\d+)/:month(\\d+)`" will match "`/blog/2012/02`".
A group can also be made <span class="allow-2119">optional</span>, or repeated, by using a modifier. For example, the pathname pattern "`/products/:id?"` will match both "`/products`" and "`/products/2`" (but not "`/products/`"). In the pathname specifically, groups automatically require a leading `/`; to avoid this, the group can be explicitly deliminated, as in the pathname pattern "`/products/{:id}?`".
A full wildcard `*` can also be used to match as much as possible, as in the pathname pattern "`/products/*`".
</div>
<h3 id=parsing-pattern-strings>Parsing pattern strings</h3>
<h4 id=tokens>Tokens</h4>
A <dfn>token list</dfn> is a [=list=] containing zero or more [=token=] [=structs=].
A <dfn>token</dfn> is a [=struct=] representing a single lexical token within a [=/pattern string=].
A [=token=] has an associated <dfn for=token>type</dfn>, a string, initially "<a for=token/type>`invalid-char`</a>". It must be one of the following:
<dl>
<dt>"<dfn for=token/type>`open`</dfn>"</dt>
<dd>The [=token=] represents a U+007B (`{`) code point.
<dt>"<dfn for=token/type>`close`</dfn>"</dt>
<dd>The [=token=] represents a U+007D (`}`) code point.
<dt>"<dfn for=token/type>`regexp`</dfn>"</dt>
<dd>The [=token=] represents a string of the form "`(<regular expression>)`". The regular expression is required to consist of only ASCII code points.
<dt>"<dfn for=token/type>`name`</dfn>"</dt>
<dd>The [=token=] represents a string of the form "`:<name>`". The name value is restricted to code points that are consistent with JavaScript identifiers.
<dt>"<dfn for=token/type>`char`</dfn>"</dt>
<dd>The [=token=] represents a valid pattern code point without any special syntactical meaning.
<dt>"<dfn for=token/type>`escaped-char`</dfn>"</dt>
<dd>The [=token=] represents a code point escaped using a backslash like "`\<char>`".
<dt>"<dfn for=token/type>`other-modifier`</dfn>"</dt>
<dd>The [=token=] represents a matching group modifier that is either the U+003F (`?`) or U+002B (`+`) code points.
<dt>"<dfn for=token/type>`asterisk`</dfn>"</dt>