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<!DOCTYPE html><html lang=en><head>
<meta content="text/html; charset=utf-8" http-equiv=Content-Type>
<title>CSS Syntax Module Level 3</title>
<link href=../default.css rel=stylesheet type=text/css>
<link href=../csslogo.ico rel="shortcut icon" type=image/x-icon>
<link href=https://www.w3.org/StyleSheets/TR/W3C-ED rel=stylesheet type=text/css>
<link href=railroad-diagrams.css rel=stylesheet type=text/css>
</head>
<body class=h-entry>
<div class=head>
<p data-fill-with=logo><a class=logo href=http://www.w3.org/>
<img alt=W3C height=48 src=http://www.w3.org/Icons/w3c_home width=72>
</a></p>
<h1 class="p-name no-ref" id=title>CSS Syntax Module Level 3</h1>
<h2 class="no-num no-toc no-ref heading settled heading" id=subtitle><span class=content>Editor’s Draft,
<span class=dt-updated><span class=value-title title=20131029>29 October 2013</span></span></span></h2>
<div data-fill-with=spec-metadata><dl><dt>This version:<dd><a class=u-url href=http://dev.w3.org/csswg/css-syntax/>http://dev.w3.org/csswg/css-syntax/</a><dt>Latest version:<dd><a href=http://www.w3.org/TR/css-syntax-3/>http://www.w3.org/TR/css-syntax-3/</a><dt>Editor’s Draft:<dd><a href=http://dev.w3.org/csswg/css-syntax/>http://dev.w3.org/csswg/css-syntax/</a><dt>Previous Versions:<dd><a href=http://www.w3.org/TR/2013/WD-css-syntax-3-20130919/ rel=previous>http://www.w3.org/TR/2013/WD-css-syntax-3-20130919/</a>
<dt>Feedback:</dt>
<dd><a href="mailto:www-style@w3.org?subject=%5Bcss-syntax%5D%20feedback">www-style@w3.org</a>
with subject line
“<kbd>[css-syntax] <var>… message topic …</var></kbd>”(<a href=http://lists.w3.org/Archives/Public/www-style/ rel=discussion>archives</a>)<dt>Test Suite:<dd>None Yet<dt>Editors:
<dd class="p-author h-card vcard"><a class="p-name fn u-url url" href=http://xanthir.com/contact/>Tab Atkins Jr.</a> (<span class="p-org org">Google</span>)<dd class="p-author h-card vcard"><a class="p-name fn u-url url" href=http://exyr.org/about/>Simon Sapin</a> (<span class="p-org org">Mozilla</span>)</dl></div>
<div data-fill-with=warning></div>
<p class=copyright data-fill-with=copyright><a href=http://www.w3.org/Consortium/Legal/ipr-notice#Copyright>Copyright</a> © 2013 <a href=http://www.w3.org/><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a href=http://www.csail.mit.edu/><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>, <a href=http://www.ercim.eu/><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href=http://www.keio.ac.jp/>Keio</a>, <a href=http://ev.buaa.edu.cn/>Beihang</a>), All Rights Reserved. W3C <a href=http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer>liability</a>, <a href=http://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks>trademark</a> and <a href=http://www.w3.org/Consortium/Legal/copyright-documents>document use</a> rules apply.</p>
<hr title="Separator for header">
</div>
<h2 class="no-num no-toc no-ref heading settled heading" id=abstract><span class=content>Abstract</span></h2>
<p class=p-summary data-fill-with=abstract>This module describes, in general terms, the basic structure and syntax of CSS stylesheets. It defines, in detail, the syntax and parsing of CSS - how to turn a stream of bytes into a meaningful stylesheet.
<a href=http://www.w3.org/TR/CSS/>CSS</a> is a language for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, in speech, etc.</p>
<h2 class="no-num no-toc no-ref heading settled heading" id=status><span class=content>Status of this document</span></h2>
<div data-fill-with=status><p>
This is a public copy of the editors’ draft.
It is provided for discussion only and may change at any moment.
Its publication here does not imply endorsement of its contents by W3C.
Don’t cite this document other than as work in progress.
<p>
The (<a href=http://lists.w3.org/Archives/Public/www-style/>archived</a>) public mailing list
<a href="mailto:www-style@w3.org?Subject=%5Bcss-syntax%5D%20PUT%20SUBJECT%20HERE">www-style@w3.org</a>
(see <a href=http://www.w3.org/Mail/Request>instructions</a>)
is preferred for discussion of this specification.
When sending e-mail,
please put the text “css-syntax” in the subject,
preferably like this:
“[css-syntax] <em>…summary of comment…</em>”
<p>
This document was produced by the <a href=http://www.w3.org/Style/CSS/members>CSS Working Group</a>
(part of the <a href=http://www.w3.org/Style/>Style Activity</a>).
<p>
This document was produced by a group operating under
the <a href=http://www.w3.org/Consortium/Patent-Policy-20040205/>5 February 2004 W3C Patent Policy</a>.
W3C maintains a <a href=http://www.w3.org/2004/01/pp-impl/32061/status rel=disclosure>public list of any patent disclosures</a>
made in connection with the deliverables of the group;
that page also includes instructions for disclosing a patent.
An individual who has actual knowledge of a patent which the individual believes contains <a href=http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential>Essential Claim(s)</a>
must disclose the information in accordance with <a href=http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure>section 6 of the W3C Patent Policy</a>.</div>
<div data-fill-with=at-risk></div>
<h2 class="no-num no-toc no-ref heading settled heading" id=contents><span class=content>Table of contents</span></h2>
<div data-fill-with=table-of-contents><ul class=toc><li><a href=#intro><span class=secno>1</span>
Introduction</a><ul class=toc><li><a href=#placement><span class=secno>1.1</span>
Module interactions</a></ul><li><a href=#syntax-description><span class=secno>2</span>
Description of CSS’s Syntax</a><ul class=toc><li><a href=#escaping><span class=secno>2.1</span>
Escaping</a><li><a href=#error-handling><span class=secno>2.2</span>
Error Handling</a></ul><li><a href=#tokenizing-and-parsing><span class=secno>3</span>
Tokenizing and Parsing CSS</a><ul class=toc><li><a href=#parsing-overview><span class=secno>3.1</span>
Overview of the Parsing Model</a><li><a href=#input-byte-stream><span class=secno>3.2</span>
The input byte stream</a><li><a href=#environment-encoding><span class=secno>3.3</span>
Environment encoding</a><ul class=toc><li><a href=#environment-encoding-at-import><span class=secno>3.3.1</span>
<span class=css data-link-type=maybe title=@import>@import</span> rules</a><li><a href=#environment-encoding-html><span class=secno>3.3.2</span>
HTML</a><li><a href=#environment-encoding-xml><span class=secno>3.3.3</span>
XML</a></ul><li><a href=#input-preprocessing><span class=secno>3.4</span>
Preprocessing the input stream</a></ul><li><a href=#tokenization><span class=secno>4</span>
Tokenization</a><ul class=toc><li><a href=#token-diagrams><span class=secno>4.1</span>
Token Railroad Diagrams</a><li><a href=#tokenizer-definitions><span class=secno>4.2</span>
Definitions</a><li><a href=#tokenizer-algorithms><span class=secno>4.3</span>
Tokenizer Algorithms</a><ul class=toc><li><a href=#consume-a-token><span class=secno>4.3.1</span>
Consume a token</a><li><a href=#consume-a-numeric-token><span class=secno>4.3.2</span>
Consume a numeric token</a><li><a href=#consume-an-ident-like-token><span class=secno>4.3.3</span>
Consume an ident-like token</a><li><a href=#consume-a-string-token><span class=secno>4.3.4</span>
Consume a string token</a><li><a href=#consume-a-url-token><span class=secno>4.3.5</span>
Consume a url token</a><li><a href=#consume-a-unicode-range-token><span class=secno>4.3.6</span>
Consume a unicode-range token</a><li><a href=#consume-an-escaped-code-point><span class=secno>4.3.7</span>
Consume an escaped code point</a><li><a href=#starts-with-a-valid-escape><span class=secno>4.3.8</span>
Check if two code points are a valid escape</a><li><a href=#would-start-an-identifier><span class=secno>4.3.9</span>
Check if three code points would start an identifier</a><li><a href=#starts-with-a-number><span class=secno>4.3.10</span>
Check if three code points would start a number</a><li><a href=#consume-a-name><span class=secno>4.3.11</span>
Consume a name</a><li><a href=#consume-a-number><span class=secno>4.3.12</span>
Consume a number</a><li><a href=#convert-a-string-to-a-number><span class=secno>4.3.13</span>
Convert a string to a number</a><li><a href=#consume-the-remnants-of-a-bad-url><span class=secno>4.3.14</span>
Consume the remnants of a bad url</a></ul></ul><li><a href=#parsing><span class=secno>5</span>
Parsing</a><ul class=toc><li><a href=#parser-diagrams><span class=secno>5.1</span>
Parser Railroad Diagrams</a><li><a href=#parser-definitions><span class=secno>5.2</span>
Definitions</a><li><a href=#parser-entry-points><span class=secno>5.3</span>
Parser Entry Points</a><ul class=toc><li><a href=#parse-a-stylesheet><span class=secno>5.3.1</span>
Parse a stylesheet</a><li><a href=#parse-a-list-of-rules><span class=secno>5.3.2</span>
Parse a list of rules</a><li><a href=#parse-a-rule><span class=secno>5.3.3</span>
Parse a rule</a><li><a href=#parse-a-declaration><span class=secno>5.3.4</span>
Parse a declaration</a><li><a href=#parse-a-list-of-declarations><span class=secno>5.3.5</span>
Parse a list of declarations</a><li><a href=#parse-a-component-value><span class=secno>5.3.6</span>
Parse a component value</a><li><a href=#parse-a-list-of-component-values><span class=secno>5.3.7</span>
Parse a list of component values</a></ul><li><a href=#parser-algorithms><span class=secno>5.4</span>
Parser Algorithms</a><ul class=toc><li><a href=#consume-a-list-of-rules><span class=secno>5.4.1</span>
Consume a list of rules</a><li><a href=#consume-an-at-rule><span class=secno>5.4.2</span>
Consume an at-rule</a><li><a href=#consume-a-qualified-rule><span class=secno>5.4.3</span>
Consume a qualified rule</a><li><a href=#consume-a-list-of-declarations><span class=secno>5.4.4</span>
Consume a list of declarations</a><li><a href=#consume-a-declaration><span class=secno>5.4.5</span>
Consume a declaration</a><li><a href=#consume-a-component-value><span class=secno>5.4.6</span>
Consume a component value</a><li><a href=#consume-a-simple-block><span class=secno>5.4.7</span>
Consume a simple block</a><li><a href=#consume-a-function><span class=secno>5.4.8</span>
Consume a function</a></ul></ul><li><a href=#anb><span class=secno>6</span>
The <var>An+B</var> microsyntax</a><ul class=toc><li><a href=#anb-syntax><span class=secno>6.1</span>
Informal Syntax Description</a><li><a href=#the-anb-type><span class=secno>6.2</span>
The <code><an+b></code> type</a></ul><li><a href=#rule-defs><span class=secno>7</span>
Defining Grammars for Rules and Other Values</a><ul class=toc><li><a href=#declaration-rule-list><span class=secno>7.1</span>
Defining Block Contents: the <span class=production data-link-type=type title="<declaration-list>"><declaration-list></span>, <span class=production data-link-type=type title="<rule-list>"><rule-list></span>, and <span class=production data-link-type=type title="<stylesheet>"><stylesheet></span> productions</a></ul><li><a href=#css-stylesheets><span class=secno>8</span>
CSS stylesheets</a><ul class=toc><li><a href=#style-rules><span class=secno>8.1</span>
Style rules</a><li><a href=#charset-rule><span class=secno>8.2</span>
The <span class=css data-link-type=maybe title=@charset>@charset</span> Rule</a></ul><li><a href=#serialization><span class=secno>9</span>
Serialization</a><ul class=toc><li><a href=#serializing-anb><span class=secno>9.1</span>
Serializing <var><an+b></var></a></ul><li><a href=#changes><span class=secno>10</span>
Changes from CSS 2.1 and Selectors Level 3</a><li><a href=#acknowledgments><span class=secno></span>
Acknowledgments</a><li><a href=#conformance><span class=secno></span>
Conformance</a><ul class=toc><li><a href=#conventions><span class=secno></span>
Document conventions</a><li><a href=#conformance-classes><span class=secno></span>
Conformance classes</a><li><a href=#partial><span class=secno></span>
Partial implementations</a><li><a href=#experimental><span class=secno></span>
Experimental implementations</a><li><a href=#testing><span class=secno></span>
Non-experimental implementations</a></ul><li><a href=#references><span class=secno></span>
References</a><ul class=toc><li><a href=#normative><span class=secno></span>
Normative References</a><li><a href=#informative><span class=secno></span>
Informative References</a></ul><li><a href=#index><span class=secno></span>
Index</a><li><a href=#property-index><span class=secno></span>
Property index</a></ul></div>
<h2 class="heading settled heading" data-level=1 id=intro><span class=secno>1 </span><span class=content>
Introduction</span><a class=self-link href=#intro></a></h2>
<p> <em>This section is not normative.</em>
<p> This module defines the abstract syntax and parsing of CSS stylesheets
and other things which use CSS syntax
(such as the HTML <code>style</code> attribute).
<p> It defines algorithms for converting a stream of Unicode <a data-link-type=dfn href=#code-point title="code points">code points</a>
(in other words, text)
into a stream of CSS tokens,
and then further into CSS objects
such as stylesheets, rules, and declarations.
<h3 class="heading settled heading" data-level=1.1 id=placement><span class=secno>1.1 </span><span class=content>
Module interactions</span><a class=self-link href=#placement></a></h3>
<p> This module defines the syntax and parsing of CSS stylesheets.
It supersedes the lexical scanner and grammar defined in CSS 2.1.
<h2 class="heading settled heading" data-level=2 id=syntax-description><span class=secno>2 </span><span class=content>
Description of CSS’s Syntax</span><a class=self-link href=#syntax-description></a></h2>
<p> <em>This section is not normative.</em>
<p> A CSS document is a series of <a data-link-type=dfn href=#qualified-rule title="qualified rules">qualified rules</a>,
which are usually style rules that apply CSS properties to elements,
and <a data-link-type=dfn href=#at-rule title=at-rules>at-rules</a>,
which define special processing rules or values for the CSS document.
<p> A qualified rule starts with a prelude
then has a {}-wrapped block containing a sequence of declarations.
The meaning of the prelude varies based on the context that the rule appears in -
for style rules, it’s a selector which specifies what elements the declarations will apply to.
Each declaration has a name,
followed by a colon and the declaration value.
Declarations are separated by semicolons.
<div class=example>
<p> A typical rule might look something like this:
<pre> p > a {
color: blue;
text-decoration: underline;
}
</pre>
<p> In the above rule, "<code>p > a</code>" is the selector,
which, if the source document is HTML,
selects any <code><a></code> elements that are children of a <code><p></code> element.
<p> "<code>color: blue;</code>" is a declaration specifying that,
for the elements that match the selector,
their <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-color-3/#propdef-color title=color>color</a> property should have the value <span class=css data-link-type=maybe title=blue>blue</span>.
Similiarly, their <a class=property data-link-type=propdesc href=http://dev.w3.org/csswg/css-text-decor-3/#text-decoration title=text-decoration>text-decoration</a> property should have the value <span class=css data-link-type=maybe title=underline>underline</span>.
</div>
<p> At-rules are all different, but they have a basic structure in common.
They start with an "@" <a data-link-type=dfn href=#code-point title="code point">code point</a> followed by their name.
Some <a data-link-type=dfn href=#at-rule title=at-rules>at-rules</a> are simple statements,
with their name followed by more CSS values to specify their behavior,
and finally ended by a semicolon.
Others are blocks;
they can have CSS values following their name,
but they end with a {}-wrapped block,
similar to a <a data-link-type=dfn href=#qualified-rule title="qualified rule">qualified rule</a>.
Even the contents of these blocks are specific to the given <a data-link-type=dfn href=#at-rule title=at-rule>at-rule</a>:
sometimes they contain a sequence of declarations, like a <a data-link-type=dfn href=#qualified-rule title="qualified rule">qualified rule</a>;
other times, they may contain additional blocks, or at-rules, or other structures altogether.
<div class=example>
<p> Here are several examples of <a data-link-type=dfn href=#at-rule title=at-rules>at-rules</a> that illustrate the varied syntax they may contain.
<pre>@import "my-styles.css";</pre>
<p> The <a class=css data-link-type=maybe href=http://dev.w3.org/csswg/css-cascade-3/#at-ruledef-import title=@import>@import</a> <a data-link-type=dfn href=#at-rule title=at-rule>at-rule</a> is a simple statement.
After its name, it takes a single string or <span class=css data-link-type=maybe title=url()>url()</span> function to indicate the stylesheet that it should import.
<pre> @page :left {
margin-left: 4cm;
margin-right: 3cm;
}
</pre>
<p> The <span class=css data-link-type=maybe title=@page>@page</span> <a data-link-type=dfn href=#at-rule title=at-rule>at-rule</a> consists of an optional page selector (the <span class=css data-link-type=maybe title=:left>:left</span> pseudoclass),
followed by a block of properties that apply to the page when printed.
In this way, it’s very similar to a normal style rule,
except that its properties don’t apply to any "element",
but rather the page itself.
<pre> @media print {
body { font-size: 10pt }
}
</pre>
<p> The <span class=css data-link-type=maybe title=@media>@media</span> <a data-link-type=dfn href=#at-rule title=at-rule>at-rule</a> begins with a media type
and a list of optional media queries.
Its block contains entire rules,
which are only applied when the <span class=css data-link-type=maybe title=@media>@media</span>s conditions are fulfilled.
</div>
<p> Property names and <a data-link-type=dfn href=#at-rule title=at-rule>at-rule</a> names are always <b>identifiers</b>,
which have to start with a letter or a hyphen followed by a letter,
and then can contain letters, numbers, hyphens, or underscores.
You can include any <a data-link-type=dfn href=#code-point title="code point">code point</a> at all,
even ones that CSS uses in its syntax,
by <a data-link-type=dfn href=#escaping0 title=escaping>escaping</a> it.
<p> The syntax of selectors is defined in the <a href=http://www.w3.org/TR/selectors/>Selectors spec</a>.
Similarly, the syntax of the wide variety of CSS values is defined in the <a href=http://www.w3.org/TR/css3-values/>Values & Units spec</a>.
The special syntaxes of individual <a data-link-type=dfn href=#at-rule title=at-rules>at-rules</a> can be found in the specs that define them.
<h3 class="heading settled heading" data-level=2.1 id=escaping><span class=secno>2.1 </span><span class=content>
Escaping</span><a class=self-link href=#escaping></a></h3>
<p> <em>This section is not normative.</em>
<p> Any Unicode <a data-link-type=dfn href=#code-point title="code point">code point</a> can be included in an identifier or quoted string
by <dfn data-dfn-type=dfn data-noexport="" id=escaping0>escaping<a class=self-link href=#escaping0></a></dfn> it.
CSS escape sequences start with a backslash (\), and continue with:
<p> <ul>
<li>
Any Unicode <a data-link-type=dfn href=#code-point title="code point">code point</a> that is not a <a data-link-type=dfn href=#hex-digit title="hex digits">hex digits</a> or a <a data-link-type=dfn href=#newline title=newline>newline</a>.
The escape sequence is replaced by that <a data-link-type=dfn href=#code-point title="code point">code point</a>.
<li>
Or one to six <a data-link-type=dfn href=#hex-digit title="hex digits">hex digits</a>, followed by an optional <a data-link-type=dfn href=#whitespace title=whitespace>whitespace</a>.
The escape sequence is replaced by the Unicode <a data-link-type=dfn href=#code-point title="code point">code point</a>
whose value is given by the hexadecimal digits.
This optional whitespace allow hexadecimal escape sequences
to be followed by "real" hex digits.
<p class=example>
An identifier with the value "&B"
could be written as <span class=css data-link-type=maybe title="\26 b">\26 B</span> or <span class=css data-link-type=maybe title=\000026b>\000026B</span>.
<p class=note>
A "real" space after the escape sequence must be doubled.
</ul>
<h3 class="heading settled heading" data-level=2.2 id=error-handling><span class=secno>2.2 </span><span class=content>
Error Handling</span><a class=self-link href=#error-handling></a></h3>
<p> <em>This section is not normative.</em>
<p> When errors occur in CSS,
the parser attempts to recover gracefully,
throwing away only the minimum amount of content
before returning to parsing as normal.
This is because errors aren’t always mistakes -
new syntax looks like an error to an old parser,
and it’s useful to be able to add new syntax to the language
without worrying about stylesheets that include it being completely broken in older UAs.
<p> The precise error-recovery behavior is detailed in the parser itself,
but it’s simple enough that a short description is fairly accurate:
<p> <ul>
<li>
At the "top level" of a stylesheet,
an <a class="production css-code" data-link-type=type href=#typedef-at-keyword-token title="<at-keyword-token>"><at-keyword-token></a> starts an at-rule.
Anything else starts a qualified rule,
and is included in the rule’s prelude.
This may produce an invalid selector,
but that’s not the concern of the CSS parser —
at worst, it means the selector will match nothing.
<li>
Once an at-rule starts,
nothing is invalid from the parser’s standpoint;
it’s all part of the at-rule’s prelude.
Encountering a <a class="production css-code" data-link-type=type href=#typedef-semicolon-token title="<semicolon-token>"><semicolon-token></a> ends the at-rule immediately,
while encountering an opening curly-brace <<{-token>> starts the at-rule’s body.
The at-rule seeks forward, matching blocks (content surrounded by (), {}, or [])
until it finds a closing curly-brace <<}-token>> that isn’t matched by anything else
or inside of another block.
The contents of the at-rule are then interpreted according to the at-rule’s own grammar.
<li>
Qualified rules work similarly,
except that semicolons don’t end them;
instead, they are just taken in as part of the rule’s prelude.
When the first {} block is found,
the contents are always interpreted as a list of declarations.
<li>
When interpreting a list of declarations,
unknown syntax at any point causes the parser to throw away whatever declaration it’s currently building,
and seek forward until it finds a semicolon (or the end of the block).
It then starts fresh, trying to parse a declaration again.
<li>
If the stylesheet ends while any rule, declaration, function, string, etc. are still open,
everything is automatically closed.
This doesn’t make them invalid,
though they may be incomplete
and thus thrown away when they are verified against their grammar.
</ul>
<h2 class="heading settled heading" data-level=3 id=tokenizing-and-parsing><span class=secno>3 </span><span class=content>
Tokenizing and Parsing CSS</span><a class=self-link href=#tokenizing-and-parsing></a></h2>
<p> User agents must use the parsing rules described in this specification
to generate the CSSOM trees from text/css resources.
Together, these rules define what is referred to as the CSS parser.
<p> This specification defines the parsing rules for CSS documents,
whether they are syntactically correct or not.
Certain points in the parsing algorithm are said to be a <dfn data-dfn-type=dfn data-noexport="" id=parse-error title="parse error">parse errors<a class=self-link href=#parse-error></a></dfn>.
The error handling for parse errors is well-defined:
user agents must either act as described below when encountering such problems,
or must abort processing at the first error that they encounter for which they do not wish to apply the rules described below.
<p> Conformance checkers must report at least one parse error condition to the user
if one or more parse error conditions exist in the document
and must not report parse error conditions
if none exist in the document.
Conformance checkers may report more than one parse error condition if more than one parse error condition exists in the document.
Conformance checkers are not required to recover from parse errors,
but if they do,
they must recover in the same way as user agents.
<h3 class="heading settled heading" data-level=3.1 id=parsing-overview><span class=secno>3.1 </span><span class=content>
Overview of the Parsing Model</span><a class=self-link href=#parsing-overview></a></h3>
<p> The input to the CSS parsing process consists of a stream of Unicode <a data-link-type=dfn href=#code-point title="code points">code points</a>,
which is passed through a tokenization stage followed by a tree construction stage.
The output is a CSSStyleSheet object.
<p class=note> Note: Implementations that do not support scripting do not have to actually create a CSSOM CSSStyleSheet object,
but the CSSOM tree in such cases is still used as the model for the rest of the specification.
<h3 class="heading settled heading" data-level=3.2 id=input-byte-stream><span class=secno>3.2 </span><span class=content>
The input byte stream</span><a class=self-link href=#input-byte-stream></a></h3>
<p> When parsing a stylesheet,
the stream of Unicode <a data-link-type=dfn href=#code-point title="code points">code points</a> that comprises the input to the tokenization stage
may be initially seen by the user agent as a stream of bytes
(typically coming over the network or from the local file system).
The bytes encode the <a data-link-type=dfn href=#code-point title="code points">code points</a> according to a particular character encoding,
which the user agent must use to decode the bytes into <a data-link-type=dfn href=#code-point title="code points">code points</a>.
<p> To decode the stream of bytes into a stream of <a data-link-type=dfn href=#code-point title="code points">code points</a>,
UAs must follow these steps.
<p> The algorithms to <dfn data-dfn-type=dfn data-noexport="" id=get-an-encoding><a href=http://encoding.spec.whatwg.org/#concept-encoding-get>get an encoding</a><a class=self-link href=#get-an-encoding></a></dfn>
and <dfn data-dfn-type=dfn data-noexport="" id=decode><a href=http://encoding.spec.whatwg.org/#decode>decode</a><a class=self-link href=#decode></a></dfn>
are defined in the <a href=http://encoding.spec.whatwg.org/>Encoding Standard</a>.
<p> First, <dfn data-dfn-type=dfn data-noexport="" id=determine-the-fallback-encoding>determine the fallback encoding<a class=self-link href=#determine-the-fallback-encoding></a></dfn>:
<ol>
<li>
If HTTP or equivalent protocol defines an encoding (e.g. via the charset parameter of the Content-Type header),
<a data-link-type=dfn href=#get-an-encoding title="get an encoding">get an encoding</a> for the specified value.
If that does not return failure,
use the return value as the fallback encoding.
<li>
Otherwise, check the byte stream. If the first several bytes match the hex sequence
<pre>40 63 68 61 72 73 65 74 20 22 (not 22)* 22 3B</pre>
<p> then <a data-link-type=dfn href=#get-an-encoding title="get an encoding">get an encoding</a> for the sequence of <code>(not 22)*</code> bytes,
decoded per <code>windows-1252</code>.
<p class=note> Note: Anything ASCII-compatible will do, so using <code>windows-1252</code> is fine.
<p class=note> Note: The byte sequence above,
when decoded as ASCII,
is the string "<code>@charset "…";</code>",
where the "…" is the sequence of bytes corresponding to the encoding’s name.
<p> If the return value was <code>utf-16</code> or <code>utf-16be</code>,
use <code>utf-8</code> as the fallback encoding;
if it was anything else except failure,
use the return value as the fallback encoding.
<p class=note> Note: This mimics HTML <code><meta></code> behavior.
<li>
Otherwise, if an <a data-link-type=dfn href=#environment-encoding0 title="environment encoding">environment encoding</a> is provided by the referring document,
use that as the fallback encoding.
<li>
Otherwise, use <code>utf-8</code> as the fallback encoding.
</ol>
<p> Then, <a data-link-type=dfn href=#decode title=decode>decode</a> the byte stream using the fallback encoding.
<p class=note> Note: the <a data-link-type=dfn href=#decode title=decode>decode</a> algorithm lets the byte order mark (BOM) take precedence,
hence the usage of the term "fallback" above.
<h3 class="heading settled heading" data-level=3.3 id=environment-encoding><span class=secno>3.3 </span><span class=content>
Environment encoding</span><a class=self-link href=#environment-encoding></a></h3>
<p>Document languages that refer to CSS stylesheets that are decoded from bytes
must define an <dfn data-dfn-type=dfn data-noexport="" id=environment-encoding0>environment encoding<a class=self-link href=#environment-encoding0></a></dfn> for each such stylesheet,
which is used as a fallback when other encoding hints are not available or can not be used.
<h4 class="heading settled heading" data-level=3.3.1 id=environment-encoding-at-import><span class=secno>3.3.1 </span><span class=content>
<a class=css data-link-type=maybe href=http://dev.w3.org/csswg/css-cascade-3/#at-ruledef-import title=@import>@import</a> rules</span><a class=self-link href=#environment-encoding-at-import></a></h4>
<p> For stylesheets referred to by an <a class=css data-link-type=maybe href=http://dev.w3.org/csswg/css-cascade-3/#at-ruledef-import title=@import>@import</a> CSS rule <a data-biblio-type=normative data-link-type=biblio href=#css3cascade title=css3cascade>[CSS3CASCADE]</a>,
the <a data-link-type=dfn href=#environment-encoding0 title="environment encoding">environment encoding</a> is the encoding of the referring stylesheet.
<p class=note> Note: this should be moved to <a data-biblio-type=informative data-link-type=biblio href=#css3cascade title=css3cascade>[CSS3CASCADE]</a>.
<h4 class="heading settled heading" data-level=3.3.2 id=environment-encoding-html><span class=secno>3.3.2 </span><span class=content>
HTML</span><a class=self-link href=#environment-encoding-html></a></h4>
<p> For stylesheets referred to by an HTML <a href=http://www.whatwg.org/specs/web-apps/current-work/multipage/links.html#link-type-stylesheet><code><link rel=stylesheet></code></a> element,
the <a data-link-type=dfn href=#environment-encoding0 title="environment encoding">environment encoding</a> is determined as follows:
<p> <ul>
<li>
<a data-link-type=dfn href=#get-an-encoding title="get an encoding">Get an encoding</a> for the value of the <code>charset</code> attribute of the element, if any.
If that does not return failure,
use the return value as the environment encoding.
<li>
Otherwise, use the encoding of the referring document.
</ul>
<p class=note> Note: this should be moved to the HTML spec.
<p class=note> Note: Even though the HTML spec marks the <code>charset</code> attribute as obsolete,
implementations still consider it as of this writing (October 2013.)
Should we drop it?
<h4 class="heading settled heading" data-level=3.3.3 id=environment-encoding-xml><span class=secno>3.3.3 </span><span class=content>
XML</span><a class=self-link href=#environment-encoding-xml></a></h4>
<p> For stylesheets referred to by an <a href=http://www.w3.org/TR/xml-stylesheet/#the-xml-stylesheet-processing-instruction><code>xml-stylesheet</code></a> processing instruction <a data-biblio-type=normative data-link-type=biblio href=#xmlstyle title=xmlstyle>[XMLSTYLE]</a>,
the <a data-link-type=dfn href=#environment-encoding0 title="environment encoding">environment encoding</a> is determined as follows:
<p> <ul>
<li>
<a data-link-type=dfn href=#get-an-encoding title="get an encoding">Get an encoding</a> for the value of the <code>charset</code> <a href=http://www.w3.org/TR/xml-stylesheet/#dt-pseudo-attribute>pseudo-attribute</a> on processing instruction, if any.
If that does not return failure,
use the return value as the environment encoding.
<li>
Otherwise, use the encoding of the referring document.
</ul>
<p class=note> Note: This should be moved to <a data-biblio-type=informative data-link-type=biblio href=#cssom title=cssom>[CSSOM]</a>.
<h3 class="heading settled heading" data-level=3.4 id=input-preprocessing><span class=secno>3.4 </span><span class=content>
Preprocessing the input stream</span><a class=self-link href=#input-preprocessing></a></h3>
<p> The input stream consists of the <a data-link-type=dfn href=#code-point title="code points">code points</a>
pushed into it as the input byte stream is decoded.
<p> Before sending the input stream to the tokenizer,
implementations must make the following <a data-link-type=dfn href=#code-point title="code point">code point</a> substitutions:
<p> <ul>
<li>
Replace any U+000D CARRIAGE RETURN (CR) <a data-link-type=dfn href=#code-point title="code point">code point</a>,
U+000C FORM FEED (FF) <a data-link-type=dfn href=#code-point title="code point">code point</a>,
or pairs of U+000D CARRIAGE RETURN (CR) followed by U+000A LINE FEED (LF)
by a single U+000A LINE FEED (LF) <a data-link-type=dfn href=#code-point title="code point">code point</a>.
<li>
Replace any U+0000 NULL <a data-link-type=dfn href=#code-point title="code point">code point</a> with U+FFFD REPLACEMENT CHARACTER (�).
</ul>
<h2 class="heading settled heading" data-level=4 id=tokenization><span class=secno>4 </span><span class=content>
Tokenization</span><a class=self-link href=#tokenization></a></h2>
<p> Implementations must act as if they used the following algorithms to tokenize CSS.
To transform a stream of <a data-link-type=dfn href=#code-point title="code points">code points</a> into a stream of tokens,
repeatedly <a data-link-type=dfn href=#consume-a-token0 title="consume a token">consume a token</a>
until an <a class="production css-code" data-link-type=type href=#typedef-eof-token title="<eof-token>"><EOF-token></a> is reached,
collecting the returned tokens into a stream.
Each call to the <a data-link-type=dfn href=#consume-a-token0 title="consume a token">consume a token</a> algorithm
returns a single token,
so it can also be used "on-demand" to tokenize a stream of <a data-link-type=dfn href=#code-point title="code points">code points</a> <em>during</em> parsing,
if so desired.
<p> The output of the tokenization step is a stream of zero or more of the following tokens:
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-ident-token><ident-token><a class=self-link href=#typedef-ident-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-function-token><function-token><a class=self-link href=#typedef-function-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-at-keyword-token><at-keyword-token><a class=self-link href=#typedef-at-keyword-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-hash-token><hash-token><a class=self-link href=#typedef-hash-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-string-token><string-token><a class=self-link href=#typedef-string-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-bad-string-token><bad-string-token><a class=self-link href=#typedef-bad-string-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-url-token><url-token><a class=self-link href=#typedef-url-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-bad-url-token><bad-url-token><a class=self-link href=#typedef-bad-url-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-delim-token><delim-token><a class=self-link href=#typedef-delim-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-number-token><number-token><a class=self-link href=#typedef-number-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-percentage-token><percentage-token><a class=self-link href=#typedef-percentage-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-dimension-token><dimension-token><a class=self-link href=#typedef-dimension-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-unicode-range-token><unicode-range-token><a class=self-link href=#typedef-unicode-range-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-include-match-token><include-match-token><a class=self-link href=#typedef-include-match-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-dash-match-token><dash-match-token><a class=self-link href=#typedef-dash-match-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-prefix-match-token><prefix-match-token><a class=self-link href=#typedef-prefix-match-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-suffix-match-token><suffix-match-token><a class=self-link href=#typedef-suffix-match-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-substring-match-token><substring-match-token><a class=self-link href=#typedef-substring-match-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-column-token><column-token><a class=self-link href=#typedef-column-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-whitespace-token><whitespace-token><a class=self-link href=#typedef-whitespace-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-cdo-token><CDO-token><a class=self-link href=#typedef-cdo-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-cdc-token><CDC-token><a class=self-link href=#typedef-cdc-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-colon-token><colon-token><a class=self-link href=#typedef-colon-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-semicolon-token><semicolon-token><a class=self-link href=#typedef-semicolon-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=typedef-comma-token><comma-token><a class=self-link href=#typedef-comma-token></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=tokendef-open-square><[-token><a class=self-link href=#tokendef-open-square></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=tokendef-close-square><]-token><a class=self-link href=#tokendef-close-square></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=tokendef-open-paren><(-token><a class=self-link href=#tokendef-open-paren></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=tokendef-close-paren><)-token><a class=self-link href=#tokendef-close-paren></a></dfn>,
<dfn class=css-code data-dfn-type=type data-export="" id=tokendef-open-curly><{-token><a class=self-link href=#tokendef-open-curly></a></dfn>,
and <dfn class=css-code data-dfn-type=type data-export="" id=tokendef-close-curly><}-token><a class=self-link href=#tokendef-close-curly></a></dfn>.
<p> <ul>
<li>
<a class="production css-code" data-link-type=type href=#typedef-ident-token title="<ident-token>"><ident-token></a>, <a class="production css-code" data-link-type=type href=#typedef-function-token title="<function-token>"><function-token></a>, <a class="production css-code" data-link-type=type href=#typedef-at-keyword-token title="<at-keyword-token>"><at-keyword-token></a>, <a class="production css-code" data-link-type=type href=#typedef-hash-token title="<hash-token>"><hash-token></a>, <a class="production css-code" data-link-type=type href=#typedef-string-token title="<string-token>"><string-token></a>, and <a class="production css-code" data-link-type=type href=#typedef-url-token title="<url-token>"><url-token></a> have a value composed of zero or more <a data-link-type=dfn href=#code-point title="code points">code points</a>.
Additionally, hash tokens have a type flag set to either "id" or "unrestricted". The type flag defaults to "unrestricted" if not otherwise set.
<li>
<a class="production css-code" data-link-type=type href=#typedef-delim-token title="<delim-token>"><delim-token></a> has a value composed of a single <a data-link-type=dfn href=#code-point title="code point">code point</a>.
<li>
<a class="production css-code" data-link-type=type href=#typedef-number-token title="<number-token>"><number-token></a>, <a class="production css-code" data-link-type=type href=#typedef-percentage-token title="<percentage-token>"><percentage-token></a>, and <a class="production css-code" data-link-type=type href=#typedef-dimension-token title="<dimension-token>"><dimension-token></a> have a representation composed of one or more <a data-link-type=dfn href=#code-point title="code points">code points</a>, and a numeric value.
<a class="production css-code" data-link-type=type href=#typedef-number-token title="<number-token>"><number-token></a> and <a class="production css-code" data-link-type=type href=#typedef-dimension-token title="<dimension-token>"><dimension-token></a> additionally have a type flag set to either "integer" or "number". The type flag defaults to "integer" if not otherwise set.
<a class="production css-code" data-link-type=type href=#typedef-dimension-token title="<dimension-token>"><dimension-token></a> additionally have a unit composed of one or more <a data-link-type=dfn href=#code-point title="code points">code points</a>.
<li>
<a class="production css-code" data-link-type=type href=#typedef-unicode-range-token title="<unicode-range-token>"><unicode-range-token></a> has
a <dfn data-dfn-type=dfn data-noexport="" id=unicode-range-start title="start of the range">start<a class=self-link href=#unicode-range-start></a></dfn>
and an <dfn data-dfn-type=dfn data-noexport="" id=unicode-range-end title="end of the range">end<a class=self-link href=#unicode-range-end></a></dfn>,
a pair of integers.
</ul>
<p class=note> Note: The type flag of hash tokens is used in the Selectors syntax <a data-biblio-type=informative data-link-type=biblio href=#select title=select>[SELECT]</a>.
Only hash tokens with the "id" type are valid <a href=http://www.w3.org/TR/selectors/#id-selectors>ID selectors</a>.
<p class=note> Note: As a technical note,
the tokenizer defined here requires only three <a data-link-type=dfn href=#code-point title="code points">code points</a> of look-ahead.
The tokens it produces are designed to allow Selectors to be parsed with one token of look-ahead,
and additional tokens may be added in the future to maintain this invariant.
<h3 class="heading settled heading" data-level=4.1 id=token-diagrams><span class=secno>4.1 </span><span class=content>
Token Railroad Diagrams</span><a class=self-link href=#token-diagrams></a></h3>
<p> <em>This section is non-normative.</em>
<p> This section presents an informative view of the tokenizer,
in the form of railroad diagrams.
Railroad diagrams are more compact than an explicit parser,
but often easier to read than an regular expression.
<p> These diagrams are <em>informative</em> and <em>incomplete</em>;
they describe the grammar of "correct" tokens,
but do not describe error-handling at all.
They are provided solely to make it easier to get an intuitive grasp of the syntax of each token.
<p> Diagrams with names such as <em><foo-token></em> represent tokens.
The rest are productions referred to by other diagrams.
<dl>
<dt>comment
<dd>
<style scoped>svg.railroad-diagram{background-color:hsl(30,20%,95%);}svg.railroad-diagram path{stroke-width:3;stroke:black;fill:rgba(0,0,0,0);}svg.railroad-diagram text{font:bold 14px monospace;text-anchor:middle;}svg.railroad-diagram text.label{text-anchor:start;}svg.railroad-diagram text.comment{font:italic 12px monospace;}svg.railroad-diagram rect{stroke-width:3;stroke:black;fill:hsl(120,100%,90%);}</style><svg class=railroad-diagram height=81 viewBox="0 0 497 81" width=497>
<g transform="translate(.5 .5)">
<path d="M 20 31 v 20 m 10 -20 v 20 m -10 -10 h 20.5">
</path><path d="M40 41h10">
</path><g>
<path d="M50 41h0">
</path><path d="M86 41h0">
</path><rect height=22 rx=10 ry=10 width=36 x=50 y=30>
</rect><text x=68 y=45>
/*</text></g><path d="M86 41h10">
</path><g>
<path d="M96 41h0">
</path><path d="M400 41h0">
</path><path d="M96 41a10 10 0 0 0 10 -10v0a10 10 0 0 1 10 -10">
</path><g>
<path d="M116 21h264">
</path></g><path d="M380 21a10 10 0 0 1 10 10v0a10 10 0 0 0 10 10">
</path><path d="M96 41h20">
</path><g>
<path d="M116 41h0">
</path><path d="M380 41h0">
</path><path d="M116 41h10">
</path><g>
<path d="M126 41h0">
</path><path d="M370 41h0">
</path><rect height=22 width=244 x=126 y=30>
</rect><text x=248 y=45>
anything but * followed by /</text></g><path d="M370 41h10">
</path><path d="M126 41a10 10 0 0 0 -10 10v0a10 10 0 0 0 10 10">
</path><g>
<path d="M126 61h244">
</path></g><path d="M370 61a10 10 0 0 0 10 -10v0a10 10 0 0 0 -10 -10">
</path></g><path d="M380 41h20">
</path></g><path d="M400 41h10">
</path><g>
<path d="M410 41h0">
</path><path d="M446 41h0">
</path><rect height=22 rx=10 ry=10 width=36 x=410 y=30>
</rect><text x=428 y=45>
*/</text></g><path d="M446 41h10">
</path><path d="M 456 41 h 20 m -10 -10 v 20 m 10 -20 v 20">
</path></g></svg>
<dt>newline
<dd>
<style scoped>svg.railroad-diagram{background-color:hsl(30,20%,95%);}svg.railroad-diagram path{stroke-width:3;stroke:black;fill:rgba(0,0,0,0);}svg.railroad-diagram text{font:bold 14px monospace;text-anchor:middle;}svg.railroad-diagram text.label{text-anchor:start;}svg.railroad-diagram text.comment{font:italic 12px monospace;}svg.railroad-diagram rect{stroke-width:3;stroke:black;fill:hsl(120,100%,90%);}</style><svg class=railroad-diagram height=152 viewBox="0 0 173 152" width=173>
<g transform="translate(.5 .5)">
<path d="M 20 21 v 20 m 10 -20 v 20 m -10 -10 h 20.5">
</path><g>
<path d="M40 31h0">
</path><path d="M132 31h0">
</path><path d="M40 31h20">
</path><g>
<path d="M60 31h8">
</path><path d="M104 31h8">
</path><rect height=22 rx=10 ry=10 width=36 x=68 y=20>
</rect><text x=86 y=35>
\n</text></g><path d="M112 31h20">
</path><path d="M40 31a10 10 0 0 1 10 10v10a10 10 0 0 0 10 10">
</path><g>
<path d="M60 61h0">
</path><path d="M112 61h0">
</path><rect height=22 rx=10 ry=10 width=52 x=60 y=50>
</rect><text x=86 y=65>
\r\n</text></g><path d="M112 61a10 10 0 0 0 10 -10v-10a10 10 0 0 1 10 -10">
</path><path d="M40 31a10 10 0 0 1 10 10v40a10 10 0 0 0 10 10">
</path><g>
<path d="M60 91h8">
</path><path d="M104 91h8">
</path><rect height=22 rx=10 ry=10 width=36 x=68 y=80>
</rect><text x=86 y=95>
\r</text></g><path d="M112 91a10 10 0 0 0 10 -10v-40a10 10 0 0 1 10 -10">
</path><path d="M40 31a10 10 0 0 1 10 10v70a10 10 0 0 0 10 10">
</path><g>
<path d="M60 121h8">
</path><path d="M104 121h8">
</path><rect height=22 rx=10 ry=10 width=36 x=68 y=110>
</rect><text x=86 y=125>
\f</text></g><path d="M112 121a10 10 0 0 0 10 -10v-70a10 10 0 0 1 10 -10">
</path></g><path d="M 132 31 h 20 m -10 -10 v 20 m 10 -20 v 20">
</path></g></svg>
<dt>whitespace
<dd>
<style scoped>svg.railroad-diagram{background-color:hsl(30,20%,95%);}svg.railroad-diagram path{stroke-width:3;stroke:black;fill:rgba(0,0,0,0);}svg.railroad-diagram text{font:bold 14px monospace;text-anchor:middle;}svg.railroad-diagram text.label{text-anchor:start;}svg.railroad-diagram text.comment{font:italic 12px monospace;}svg.railroad-diagram rect{stroke-width:3;stroke:black;fill:hsl(120,100%,90%);}</style><svg class=railroad-diagram height=122 viewBox="0 0 197 122" width=197>
<g transform="translate(.5 .5)">
<path d="M 20 21 v 20 m 10 -20 v 20 m -10 -10 h 20.5">
</path><g>
<path d="M40 31h0">
</path><path d="M156 31h0">
</path><path d="M40 31h20">
</path><g>
<path d="M60 31h8">
</path><path d="M128 31h8">
</path><rect height=22 rx=10 ry=10 width=60 x=68 y=20>
</rect><text x=98 y=35>
space</text></g><path d="M136 31h20">
</path><path d="M40 31a10 10 0 0 1 10 10v10a10 10 0 0 0 10 10">
</path><g>
<path d="M60 61h20">
</path><path d="M116 61h20">
</path><rect height=22 rx=10 ry=10 width=36 x=80 y=50>
</rect><text x=98 y=65>
\t</text></g><path d="M136 61a10 10 0 0 0 10 -10v-10a10 10 0 0 1 10 -10">
</path><path d="M40 31a10 10 0 0 1 10 10v40a10 10 0 0 0 10 10">
</path><g>
<path d="M60 91h0">
</path><path d="M136 91h0">
</path><rect height=22 width=76 x=60 y=80>
</rect><text x=98 y=95>
newline</text></g><path d="M136 91a10 10 0 0 0 10 -10v-40a10 10 0 0 1 10 -10">
</path></g><path d="M 156 31 h 20 m -10 -10 v 20 m 10 -20 v 20">
</path></g></svg>
<dt>hex digit
<dd>
<style scoped>svg.railroad-diagram{background-color:hsl(30,20%,95%);}svg.railroad-diagram path{stroke-width:3;stroke:black;fill:rgba(0,0,0,0);}svg.railroad-diagram text{font:bold 14px monospace;text-anchor:middle;}svg.railroad-diagram text.label{text-anchor:start;}svg.railroad-diagram text.comment{font:italic 12px monospace;}svg.railroad-diagram rect{stroke-width:3;stroke:black;fill:hsl(120,100%,90%);}</style><svg class=railroad-diagram height=62 viewBox="0 0 233 62" width=233>
<g transform="translate(.5 .5)">
<path d="M 20 21 v 20 m 10 -20 v 20 m -10 -10 h 20.5">
</path><path d="M40 31h10">
</path><g>
<path d="M50 31h0">
</path><path d="M182 31h0">
</path><rect height=22 width=132 x=50 y=20>
</rect><text x=116 y=35>
0-9 a-f or A-F</text></g><path d="M182 31h10">
</path><path d="M 192 31 h 20 m -10 -10 v 20 m 10 -20 v 20">
</path></g></svg>
<dt>escape
<dd>
<style scoped>svg.railroad-diagram{background-color:hsl(30,20%,95%);}svg.railroad-diagram path{stroke-width:3;stroke:black;fill:rgba(0,0,0,0);}svg.railroad-diagram text{font:bold 14px monospace;text-anchor:middle;}svg.railroad-diagram text.label{text-anchor:start;}svg.railroad-diagram text.comment{font:italic 12px monospace;}svg.railroad-diagram rect{stroke-width:3;stroke:black;fill:hsl(120,100%,90%);}</style><svg class=railroad-diagram height=122 viewBox="0 0 441 122" width=441>
<g transform="translate(.5 .5)">
<path d="M 20 21 v 20 m 10 -20 v 20 m -10 -10 h 20.5">
</path><path d="M40 31h10">
</path><g>
<path d="M50 31h0">
</path><path d="M78 31h0">
</path><rect height=22 rx=10 ry=10 width=28 x=50 y=20>
</rect><text x=64 y=35>
\</text></g><path d="M78 31h10">
</path><g>
<path d="M88 31h0">
</path><path d="M400 31h0">
</path><path d="M88 31h20">
</path><g>
<path d="M108 31h30">
</path><path d="M350 31h30">
</path><rect height=22 width=212 x=138 y=20>
</rect><text x=244 y=35>
not newline or hex digit</text></g><path d="M380 31h20">
</path><path d="M88 31a10 10 0 0 1 10 10v10a10 10 0 0 0 10 10">
</path><g>
<path d="M108 61h0">
</path><path d="M380 61h0">
</path><path d="M108 61h10">
</path><g>
<path d="M118 61h0">
</path><path d="M230 61h0">
</path><path d="M118 61h10">
</path><g>
<path d="M128 61h0">
</path><path d="M220 61h0">
</path><rect height=22 width=92 x=128 y=50>
</rect><text x=174 y=65>
hex digit</text></g><path d="M220 61h10">
</path><path d="M128 61a10 10 0 0 0 -10 10v10a10 10 0 0 0 10 10">
</path><g>
<path d="M128 91h9">
</path><path d="M210 91h9">
</path><text class=comment x=174 y=96>
1-6 times</text></g><path d="M220 91a10 10 0 0 0 10 -10v-10a10 10 0 0 0 -10 -10">
</path></g><path d="M230 61h10">
</path><g>
<path d="M240 61h0">
</path><path d="M380 61h0">
</path><path d="M240 61h20">
</path><g>
<path d="M260 61h100">
</path></g><path d="M360 61h20">
</path><path d="M240 61a10 10 0 0 1 10 10v0a10 10 0 0 0 10 10">
</path><g>
<path d="M260 81h0">
</path><path d="M360 81h0">
</path><rect height=22 width=100 x=260 y=70>
</rect><text x=310 y=85>
whitespace</text></g><path d="M360 81a10 10 0 0 0 10 -10v0a10 10 0 0 1 10 -10">
</path></g></g><path d="M380 61a10 10 0 0 0 10 -10v-10a10 10 0 0 1 10 -10">
</path></g><path d="M 400 31 h 20 m -10 -10 v 20 m 10 -20 v 20">
</path></g></svg>
<dt><whitespace-token>
<dd>
<style scoped>svg.railroad-diagram{background-color:hsl(30,20%,95%);}svg.railroad-diagram path{stroke-width:3;stroke:black;fill:rgba(0,0,0,0);}svg.railroad-diagram text{font:bold 14px monospace;text-anchor:middle;}svg.railroad-diagram text.label{text-anchor:start;}svg.railroad-diagram text.comment{font:italic 12px monospace;}svg.railroad-diagram rect{stroke-width:3;stroke:black;fill:hsl(120,100%,90%);}</style><svg class=railroad-diagram height=71 viewBox="0 0 221 71" width=221>
<g transform="translate(.5 .5)">
<path d="M 20 21 v 20 m 10 -20 v 20 m -10 -10 h 20.5">
</path><path d="M40 31h10">
</path><g>
<path d="M50 31h0">
</path><path d="M170 31h0">
</path><path d="M50 31h10">
</path><g>
<path d="M60 31h0">
</path><path d="M160 31h0">
</path><rect height=22 width=100 x=60 y=20>
</rect><text x=110 y=35>
whitespace</text></g><path d="M160 31h10">
</path><path d="M60 31a10 10 0 0 0 -10 10v0a10 10 0 0 0 10 10">
</path><g>
<path d="M60 51h100">
</path></g><path d="M160 51a10 10 0 0 0 10 -10v0a10 10 0 0 0 -10 -10">
</path></g><path d="M170 31h10">
</path><path d="M 180 31 h 20 m -10 -10 v 20 m 10 -20 v 20">
</path></g></svg>
<dt>ws*
<dd>
<style scoped>svg.railroad-diagram{background-color:hsl(30,20%,95%);}svg.railroad-diagram path{stroke-width:3;stroke:black;fill:rgba(0,0,0,0);}svg.railroad-diagram text{font:bold 14px monospace;text-anchor:middle;}svg.railroad-diagram text.label{text-anchor:start;}svg.railroad-diagram text.comment{font:italic 12px monospace;}svg.railroad-diagram rect{stroke-width:3;stroke:black;fill:hsl(120,100%,90%);}</style><svg class=railroad-diagram height=81 viewBox="0 0 305 81" width=305>
<g transform="translate(.5 .5)">
<path d="M 20 31 v 20 m 10 -20 v 20 m -10 -10 h 20.5">
</path><g>
<path d="M40 41h0">
</path><path d="M264 41h0">
</path><path d="M40 41a10 10 0 0 0 10 -10v0a10 10 0 0 1 10 -10">
</path><g>
<path d="M60 21h184">
</path></g><path d="M244 21a10 10 0 0 1 10 10v0a10 10 0 0 0 10 10">
</path><path d="M40 41h20">
</path><g>
<path d="M60 41h0">
</path><path d="M244 41h0">
</path><path d="M60 41h10">
</path><g>
<path d="M70 41h0">
</path><path d="M234 41h0">
</path><rect height=22 width=164 x=70 y=30>
</rect><text x=152 y=45>
<whitespace-token></text></g><path d="M234 41h10">
</path><path d="M70 41a10 10 0 0 0 -10 10v0a10 10 0 0 0 10 10">
</path><g>
<path d="M70 61h164">
</path></g><path d="M234 61a10 10 0 0 0 10 -10v0a10 10 0 0 0 -10 -10">
</path></g><path d="M244 41h20">
</path></g><path d="M 264 41 h 20 m -10 -10 v 20 m 10 -20 v 20">
</path></g></svg>
<dt><ident-token>
<dd>
<style scoped>svg.railroad-diagram{background-color:hsl(30,20%,95%);}svg.railroad-diagram path{stroke-width:3;stroke:black;fill:rgba(0,0,0,0);}svg.railroad-diagram text{font:bold 14px monospace;text-anchor:middle;}svg.railroad-diagram text.label{text-anchor:start;}svg.railroad-diagram text.comment{font:italic 12px monospace;}svg.railroad-diagram rect{stroke-width:3;stroke:black;fill:hsl(120,100%,90%);}</style><svg class=railroad-diagram height=110 viewBox="0 0 729 110" width=729>
<g transform="translate(.5 .5)">
<path d="M 20 31 v 20 m 10 -20 v 20 m -10 -10 h 20.5">
</path><g>
<path d="M40 41h0">
</path><path d="M108 41h0">
</path><path d="M40 41h20">
</path><g>
<path d="M60 41h28">
</path></g><path d="M88 41h20">
</path><path d="M40 41a10 10 0 0 1 10 10v0a10 10 0 0 0 10 10">
</path><g>
<path d="M60 61h0">
</path><path d="M88 61h0">
</path><rect height=22 rx=10 ry=10 width=28 x=60 y=50>
</rect><text x=74 y=65>
-</text></g><path d="M88 61a10 10 0 0 0 10 -10v0a10 10 0 0 1 10 -10">
</path></g><g>
<path d="M108 41h0">
</path><path d="M344 41h0">
</path><path d="M108 41h20">
</path><g>
<path d="M128 41h0">
</path><path d="M324 41h0">
</path><rect height=22 width=196 x=128 y=30>
</rect><text x=226 y=45>
a-z A-Z _ or non-ASCII</text></g><path d="M324 41h20">
</path><path d="M108 41a10 10 0 0 1 10 10v10a10 10 0 0 0 10 10">
</path><g>
<path d="M128 71h64">
</path><path d="M260 71h64">
</path><rect height=22 width=68 x=192 y=60>
</rect><text x=226 y=75>
escape</text></g><path d="M324 71a10 10 0 0 0 10 -10v-10a10 10 0 0 1 10 -10">
</path></g><g>
<path d="M344 41h0">
</path><path d="M688 41h0">
</path><path d="M344 41a10 10 0 0 0 10 -10v0a10 10 0 0 1 10 -10">
</path><g>
<path d="M364 21h304">
</path></g><path d="M668 21a10 10 0 0 1 10 10v0a10 10 0 0 0 10 10">
</path><path d="M344 41h20">
</path><g>
<path d="M364 41h0">
</path><path d="M668 41h0">
</path><path d="M364 41h10">
</path><g>
<path d="M374 41h0">
</path><path d="M658 41h0">
</path><path d="M374 41h20">
</path><g>
<path d="M394 41h0">
</path><path d="M638 41h0">
</path><rect height=22 width=244 x=394 y=30>
</rect><text x=516 y=45>
a-z A-Z 0-9 _ - or non-ASCII</text></g><path d="M638 41h20">
</path><path d="M374 41a10 10 0 0 1 10 10v10a10 10 0 0 0 10 10">
</path><g>
<path d="M394 71h88">
</path><path d="M550 71h88">
</path><rect height=22 width=68 x=482 y=60>
</rect><text x=516 y=75>
escape</text></g><path d="M638 71a10 10 0 0 0 10 -10v-10a10 10 0 0 1 10 -10">
</path></g><path d="M658 41h10">
</path><path d="M374 41a10 10 0 0 0 -10 10v29a10 10 0 0 0 10 10">
</path><g>
<path d="M374 90h284">
</path></g><path d="M658 90a10 10 0 0 0 10 -10v-29a10 10 0 0 0 -10 -10">
</path></g><path d="M668 41h20">
</path></g><path d="M 688 41 h 20 m -10 -10 v 20 m 10 -20 v 20">
</path></g></svg>
<dt><function-token>
<dd>
<style scoped>svg.railroad-diagram{background-color:hsl(30,20%,95%);}svg.railroad-diagram path{stroke-width:3;stroke:black;fill:rgba(0,0,0,0);}svg.railroad-diagram text{font:bold 14px monospace;text-anchor:middle;}svg.railroad-diagram text.label{text-anchor:start;}svg.railroad-diagram text.comment{font:italic 12px monospace;}svg.railroad-diagram rect{stroke-width:3;stroke:black;fill:hsl(120,100%,90%);}</style><svg class=railroad-diagram height=62 viewBox="0 0 273 62" width=273>
<g transform="translate(.5 .5)">
<path d="M 20 21 v 20 m 10 -20 v 20 m -10 -10 h 20.5">
</path><path d="M40 31h10">
</path><g>
<path d="M50 31h0">
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