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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<!-- vim:expandtab:tabstop=2:shiftwidth=2:textwidth=72:
-->
<html><!-- the command line to process is this is:
num -l 2 template.html | toc -l 2 | incl | xref | index |\
perl -I../bin ../bin/propindex | cite-mkbib ../biblio.ref \
>template-processed.html
To do: add longdesc
-->
<head>
<title>CSS Syntax Module Level 3</title>
<link href="../default.css" rel=stylesheet type="text/css">
<link href="http://www.w3.org/StyleSheets/TR/W3C-WD" rel=stylesheet
type="text/css">
<body>
<div class=head>
<p><a class=logo href="http://www.w3.org/" rel=home><img alt=W3C height=48
src="http://www.w3.org/Icons/w3c_home" width=72></a><a class=logo
href="../" rel=in-activity><img alt=" CSS WG" height=48
src="../../../Woolly/woolly-icon.png" width=72></a></p>
<h1>CSS Syntax Module Level 3</h1>
<h2 class="no-num no-toc" id=w3c-working-draft-date-13-august-2003>W3C
Working Draft 12 April 2012</h2>
<dl>
<dt>This version:
<dd><a
href="http://www.w3.org/TR/2012/WD-css3-syntax-[ISODATE]">http://www.w3.org/TR/2012/WD-css3-syntax-[ISODATE]</a>
<dt>Latest version:
<dd><a
href="http://www.w3.org/TR/css3-syntax">http://www.w3.org/TR/css3-syntax</a>
<dt>Previous version:
<dd><a
href="http://www.w3.org/TR/2003/WD-css3-syntax-20030813">http://www.w3.org/TR/2003/WD-css3-syntax-20030813</a>
<dt>Editor:
<dd><a href="http://dbaron.org/">L. David Baron</a>, <<a
href="mailto:dbaron@dbaron.org">dbaron@dbaron.org</a>>
<dt>Additional Contributors:
<dd>Original CSS2 Authors
<dd>Bert Bos (W3C), <<a href="mailto:bert@w3.org">bert@w3.org</a>>
<dd>Peter Linss (Netscape)
</dl>
<!--begin-copyright-->
<p class=copyright><a
href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
rel=license>Copyright</a> © 2012 <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>), 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>
<!--end-copyright-->
<hr title="Separator for header">
</div>
<p
style="background: #fdd; color: red; font-weight: bold; text-align: center; padding: .5em; border: thick solid red; border-radius: 1em; position: fixed; bottom: 1em; left: 1em; right: 1em;">This
specification is not being actively maintained, and should not be used as
a guide for implementations. It may be revived in the future, but for now
should be considered obsolete. <br>
If you have questions or comments on this specification, please send an
email to the CSS Working Group's mailing list at <a
href="mailto:www-style@w3.org">www-style@w3.org</a>. (Before sending mail
for the first time, you have to subscribe at <a
href="http://lists.w3.org/Archives/Public/www-style/">http://lists.w3.org/Archives/Public/www-style/</a>.)
<h2 class="no-num no-toc" id=abstract>Abstract</h2>
<p>This CSS3 module describes the basic structure of CSS style sheets, some
of the details of the syntax, and the rules for parsing CSS style sheets.
It also describes (in some cases, informatively) how stylesheets can be
linked to documents and how those links can be media-dependent. Additional
details of the syntax of some parts of CSS described in other modules will
be described in those modules. The selectors module has a grammar for
selectors. Modules that define properties give the grammar for the values
of those properties, in a format described in this document.
<h2 class="no-num no-toc" id=status>Status of this document</h2>
<p><em>This section describes the status of this document at the time of
its publication. Other documents may supersede this document. A list of
current W3C publications and the latest revision of this technical report
can be found in the <a href="http://www.w3.org/TR/">W3C technical reports
index</a> at http://www.w3.org/TR/. The latest revision can also be found
by following the "Latest Version" link above.</em>
<p> This document is a draft of one of the modules of CSS Level 3 (CSS3).
Some parts of the document are derived from the CSS Level 1 and CSS Level
2 recommendations, and those parts are thus relatively stable. However, it
is otherwise an early draft, and considerable revision is expected in
later drafts, especially in formalization of error handling behavior, the
conformance requirements for partial implementations (given the
modularization of CSS3), and integration with other CSS3 modules.
<p>This document is a working draft of the CSS working group which is part
of the <a href="http://www.w3.org/Style/">style activity</a> (see <a
href="http://www.w3.org/Style/Activity">summary</a>).
<p>The working group would like to receive feedback: discussion takes place
on the (<a
href="http://lists.w3.org/Archives/Public/www-style/">archived</a>) public
mailing list <a
href="http://www.w3.org/Mail/Lists.html#www-style">www-style@w3.org</a>
(see <a href="http://www.w3.org/Mail/Request">instructions</a>). W3C
Members can also send comments directly to the CSS working group.
<p>This is a draft document and may be updated, replaced or obsoleted by
other documents at any time. It is inappropriate to cite this document as
other than work in progress. Its publication does not imply endorsement by
the W3C membership or the <a href="http://www.w3.org/Style/Group/">CSS
& FP Working Group</a> (<a
href="http://cgi.w3.org/MemberAccess/AccessRequest">members only</a>).
<p>Patent disclosures relevant to CSS may be found on the Working Group's
public <a href="http://www.w3.org/Style/CSS/Disclosures"
rel=disclosure>patent disclosure page.</a>
<p>This document may be available in translations in the future. The
English version of this specification is the only normative version.
<h2 class="no-num no-toc" id=contents>Table of contents</h2>
<!--begin-toc-->
<ul class=toc>
<li><a href="#dependencies-on-other-modules"><span class=secno>1.
</span>Dependencies on other modules</a>
<li><a href="#introduction"><span class=secno>2. </span>Introduction</a>
<li><a href="#css-style-sheet-representation"><span class=secno>3.
</span>CSS style sheet representation</a>
<ul class=toc>
<li><a href="#referring-to-characters-not-represented-"><span
class=secno>3.1. </span>Referring to characters not represented in a
character encoding</a>
<li><a href="#the-textcss-content-type"><span class=secno>3.2.
</span>The text/css content type</a>
</ul>
<li><a href="#syntax"><span class=secno>4. </span>General syntax of
CSS</a>
<ul class=toc>
<li><a href="#characters"><span class=secno>4.1. </span>Characters and
case</a>
<li><a href="#tokenization"><span class=secno>4.2.
</span>Tokenization</a>
<li><a href="#grammar"><span class=secno>4.3. </span>Grammar</a>
<ul class=toc>
<li><a href="#principles-of-css-error-handling"><span
class=secno>4.3.1. </span>Principles of CSS error handling</a>
<li><a href="#style-sheets"><span class=secno>4.3.2. </span>Style
sheets</a>
</ul>
<li><a href="#keywords"><span class=secno>4.4. </span>Keywords</a>
<li><a href="#statements"><span class=secno>4.5. </span>Statements</a>
<li><a href="#at-rules"><span class=secno>4.6. </span>At-rules</a>
<li><a href="#blocks"><span class=secno>4.7. </span>Blocks</a>
<li><a href="#rule-sets-declaration-blocks-and-selecto"><span
class=secno>4.8. </span>Rule sets, declaration blocks, and
selectors</a>
<li><a href="#declarations"><span class=secno>4.9. </span>Declarations
and properties</a>
<li><a href="#comments"><span class=secno>4.10. </span>Comments</a>
</ul>
<li><a href="#error-handling"><span class=secno>5. </span>Rules for
handling parsing errors or unsupported features</a>
<ul class=toc>
<li><a href="#partial-implementations"><span class=secno>5.1.
</span>Partial implementations</a>
</ul>
<li><a href="#vendor-specific-extensions"><span class=secno>6.
</span>Vendor-specific extensions</a>
<ul class=toc>
<li><a href="#historical-notes"><span class=secno>6.1. </span>Historical
notes</a>
</ul>
<li><a href="#conf"><span class=secno>7. </span>Conformance</a>
<ul class=toc>
<li><a href="#definitions"><span class=secno>7.1. </span>Definitions</a>
<li><a href="#conf-UA"><span class=secno>7.2. </span>User agent
conformance</a>
<ul class=toc>
<li><a href="#error-conditions"><span class=secno>7.2.1. </span>Error
conditions</a>
</ul>
<li&g
F882
t;<a href="#conf-SS"><span class=secno>7.3. </span>Style sheet
conformance</a>
<li><a href="#conf-AT"><span class=secno>7.4. </span>Authoring tool
conformance</a>
</ul>
<li><a href="#property-defs"><span class=secno>8. </span>Format of
property definitions in other modules</a>
<ul class=toc>
<li><a href="#property-def-value"><span class=secno>8.1.
</span>Value</a>
<ul class=toc>
<li><a href="#initial-and-inherit-values"><span class=secno>8.1.1.
</span><code>initial</code> and <code>inherit</code> values</a>
</ul>
<li><a href="#property-def-initial"><span class=secno>8.2.
</span>Initial</a>
<li><a href="#property-def-applies"><span class=secno>8.3.
</span>Applies to</a>
<li><a href="#property-def-inherited"><span class=secno>8.4.
</span>Inherited</a>
<li><a href="#property-def-computed"><span class=secno>8.5.
</span>Computed value</a>
<li><a href="#property-def-percent"><span class=secno>8.6.
</span>Percentage values</a>
<li><a href="#media-groups"><span class=secno>8.7. </span>Media
groups</a>
<li><a href="#shorthand-properties"><span class=secno>8.8.
</span>Shorthand properties</a>
</ul>
<li><a href="#detailed-grammar"><span class=secno>9. </span>Appendix:
Second grammar</a>
<ul class=toc>
<li><a href="#grammar0"><span class=secno>9.1. </span>Grammar</a>
<li><a href="#lexical-scanner"><span class=secno>9.2. </span>Lexical
scanner</a>
</ul>
<li class=no-num><a href="#changes-from-css2">Changes from CSS2</a>
<li class=no-num><a href="#acknowledgments">Acknowledgments</a>
<li class=no-num><a href="#references">References</a>
<ul class=toc>
<li class=no-num><a href="#normative-references">Normative
references</a>
<li class=no-num><a href="#other-references">Other references</a>
</ul>
<li class=no-num><a href="#index">Index</a>
</ul>
<!--end-toc-->
<hr>
<h2 id=dependencies-on-other-modules><span class=secno>1.
</span>Dependencies on other modules</h2>
<p>This CSS3 module depends on the following other CSS3 modules:
<ul>
<li>Selectors <a href="#SELECT"
rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a>
<li>CSS3 module: Values & Units <a href="#CSS3VAL"
rel=biblioentry>[CSS3VAL]<!--{{!CSS3VAL}}--></a>
<li>CSS3 module: Cascading & Inheritance <a href="#CSS3CASCADE"
rel=biblioentry>[CSS3CASCADE]<!--{{!CSS3CASCADE}}--></a>
</ul>
<p>It has non-normative (informative) references to the following other
CSS3 modules:
<ul>
<li>CSS3 module: Paged media <a href="#CSS3PAGE"
rel=biblioentry>[CSS3PAGE]<!--{{CSS3PAGE}}--></a>
<li>CSS3 module: Speech <a href="#CSS3SPEECH"
rel=biblioentry>[CSS3SPEECH]<!--{{CSS3SPEECH}}--></a>
<li>Media queries <a href="#MEDIAQ"
rel=biblioentry>[MEDIAQ]<!--{{MEDIAQ}}--></a>
<li>Syntax of CSS rules in HTML's "style" attribute <a
href="#CSSSTYLEATTR"
rel=biblioentry>[CSSSTYLEATTR]<!--{{CSSSTYLEATTR}}--></a>
</ul>
<h2 id=introduction><span class=secno>2. </span>Introduction</h2>
<p>This specification describes the basic syntax of CSS3 and the syntax
conventions used in the property definitions spread through the CSS3
modules. The syntax of CSS3 has some error-handling requirements for
forward-compatibility, but much of the error-handling behavior depends on
the user agent.
<h2 id=css-style-sheet-representation><span class=secno>3. </span>CSS style
sheet representation</h2>
<p>A CSS style sheet is a sequence of characters from the Universal
Character Set (see <a href="#ISO10646"
rel=biblioentry>[ISO10646]<!--{{!ISO10646}}--></a>). For transmission and
storage, these characters must be <dfn id=encoded
title="character encoding">encoded</dfn> by a character encoding that
supports the set of characters available in US-ASCII (e.g., ISO-8859-x,
Shift_JIS, etc.). A <span class=index id=BOM>byte order mark (BOM)</span>,
as described in section 2.7 of <a href="#UNICODE310"
rel=biblioentry>[UNICODE310]<!--{{!UNICODE310}}--></a>, that begins the
sequence of characters should not be considered, for purposes of applying
the grammar below, as a part of the style sheet. For a good introduction
to character sets and character encodings, please consult the HTML 4.0
specification (<a href="#HTML40"
rel=biblioentry>[HTML40]<!--{{!HTML40}}--></a>, chapter 5). See also the
XML 1.0 specification (<a href="#XML10"
rel=biblioentry>[XML10]<!--{{XML10}}--></a>, sections 2.2 and 4.3.3).
<p>When a style sheet is embedded in another document, such as in the STYLE
element or "style" attribute of HTML, the style sheet shares the character
encoding of the whole document.
<p>When a style sheet resides in a separate file, user agents must observe
the following <span class=index id=priorities
title="character encoding::user agent's determination of">priorities</span>
when determining a style sheet's <span class=index id=character-encoding
title="character encoding::default|default::character encoding">character
encoding</span> (from highest priority to lowest):
<ol>
<li>A character encoding specified by a higher level protocol (e.g., the
"charset" parameter to the MIME type specified in an HTTP "Content-Type"
field). (The HTTP protocol (<a href="#HTTP11"
rel=biblioentry>[HTTP11]<!--{{!HTTP11}}--></a>, section 3.7.1) mentions
ISO-8859-1 as a default character encoding when the "charset" parameter
is absent from the "Content-Type" header field. In practice, this
recommendation has proved useless because some servers don't allow a
"charset" parameter to be sent, and others may not be configured to send
the parameter. Therefore, user agents must not assume any default value
for the "charset" parameter, but must instead look for the <a class=index
href="#charset0" id=charset>@charset</a> rule.)
<li>The <dfn id=charset0>@charset</dfn> at-rule.
<li>Assume that the style sheet is UTF-8.
</ol>
<p>Since the third point differs from CSS1 and CSS2, authors should not
rely on user agents to assume that style sheets without encoding
information are UTF-8 encoded. Authors should specify the encoding using
one of the first two methods.
<p>At most one @charset rule may appear in an external style sheet —
it must <em>not</em> appear in an embedded style sheet — and it must
appear at the very start of the style sheet, not preceded by any
characters (except for the optional Byte Order Mark <a
href="#BOM">described above)</a>. After "@charset", authors specify the
name of a character encoding. The name must be a charset name as described
in the IANA registry (See <a href="#RFC2978"
rel=biblioentry>[RFC2978]<!--{{!RFC2978}}--></a>. Also, see <a
href="#CHARSETS" rel=biblioentry>[CHARSETS]<!--{{CHARSETS}}--></a> for a
complete list of charsets). For example:
<div class=example>
<p> @charset "ISO-8859-1";
</div>
<p>This specification does not mandate which character encodings a user
agent must support. <span class=issue>[Should we require a certain minimal
set, such as UTF-8 and UCS2?]</span>
<p>Note that reliance on the @charset construct theoretically poses a
problem since there is no <em>a priori</em> information on how it is
encoded. In practice, however, the encodings in wide use on the Internet
are either based on ASCII, UTF-16, UCS-4, or (rarely) on EBCDIC. This
means that in general, the initial byte values of a style sheet enable a
user agent to detect the encoding family reliably, which provides enough
information to decode the @charset rule, which in turn determines the
exact character encoding.
<div class=issue>[Should this specification describe how to handle encoding
errors? Can a user agent ignore the <a
href="#charset0"><code>@charset</code></a> rule if it's wrong? What if the
user agent does not support the encoding used? Should this specification
describe how to handle a <a href="#charset0"><code>@charset</code></a>
rule that specifies a character encoding that is incompatible with the
family of encodings used to decode the <a
href="#charset0"><code>@charset</code></a> rule (and BOM) itself?]</div>
<!-- More examples of good encodings to use? -IJ -->
<!-- Encodings not to use? (cf. HTML 4.0) -IJ -->
<h3 id=referring-to-characters-not-represented-><span class=secno>3.1.
</span>Referring to characters not represented in a character encoding</h3>
<p>A style sheet may have to refer to characters that cannot be represented
in the current character encoding. These characters must be written as <a
href="#character-escapes" title="backslash escapes">escaped</a> references
to ISO 10646 characters. These escapes serve the same purpose as numeric
character references in HTML or XML documents (see <a href="#HTML40"
rel=biblioentry>[HTML40]<!--{{!HTML40}}--></a>, chapters 5 and 25).
<p>The character escape mechanism should be used when only a few characters
must be represented this way. If most of a style sheet requires escaping,
authors should encode it with a more appropriate encoding (e.g., if the
style sheet contains a lot of Greek characters, authors might use
"ISO-8859-7" or "UTF-8").
<p>Intermediate processors using a different character encoding may
translate these escaped sequences into byte sequences of that encoding.
Intermediate processors must not, on the other hand, alter escape
sequences that cancel the special meaning of an ASCII character.
<p><a href="#conformance">Conforming user agents</a> must correctly map to
Unicode all characters in any character encodings that they recognize (or
they must behave as if they did).
<p>For example, a style sheet transmitted as ISO-8859-1 (Latin-1) cannot
contain Greek letters directly: "κουρος"
(Greek: "kouros") has to be written as "\3BA\3BF\3C5\3C1\3BF\3C2".
<div class=note>
<p> <em><strong>Note.</strong> In HTML 4.0, numeric character references
are interpreted in "style" attribute values but not in the content of the
STYLE element. Because of this asymmetry, we recommend that authors use
the CSS character escape mechanism rather than numeric character
references for both the "style" attribute and the STYLE element. For
example, we recommend:</em></p>
<pre class=html-example>
<span style="voice-family: D\FC rst">...</span>
</pre>
<p><em>rather than:</em></p>
<pre class=html-example>
<span style="voice-family: D&#252;rst">...</span>
</pre>
</div>
<h3 id=the-textcss-content-type><span class=secno>3.2. </sp
6D50
an>The <dfn
id=textcss>text/css</dfn> content type</h3>
<p>CSS style sheets that exist in separate files are sent over the Internet
as a sequence of bytes accompanied by encoding
information<!--(see [[!HTML40]], chapter 5)-->. The structure of the
transmission, termed a <dfn id=message-entity
title="message entity">message entity,</dfn> is defined by MIME and HTTP
1.1 (see <a href="#RFC2045"
rel=biblioentry>[RFC2045]<!--{{!RFC2045}}--></a> and <a href="#HTTP11"
rel=biblioentry>[HTTP11]<!--{{!HTTP11}}--></a>). A message entity with a
content type of "text/css" represents an independent CSS style sheet. The
"text/css" content type has been registered by RFC 2318 (<a
href="#RFC2318" rel=biblioentry>[RFC2318]<!--{{!RFC2318}}--></a>).
<h2 id=syntax><span class=secno>4. </span>General syntax of CSS</h2>
<p>This section describes a grammar (and <dfn
id=forward-compatible-parsing>forward-compatible parsing</dfn> rules)
common to any version of CSS (including CSS3). Future versions of CSS will
adhere to this core syntax, although they may add additional syntactic
constraints.
<p>See the <a href="#characters">section on characters and case</a> for
information on case-sensitivity.
<p>These descriptions are normative.
<h3 id=characters><span class=secno>4.1. </span>Characters and case</h3>
<p> The following rules always hold:
<ul>
<li>
<p>All CSS style sheets are <span class=index id=case-insensitive
title="case sensitivity">case-insensitive</span>, except for parts
that are not under the control of CSS. For example, the case-sensitivity
of values of the HTML attributes "id" and "class", of font names, and of
URIs lies outside the scope of this specification. Note in particular
that element names are case-insensitive in HTML, but case-sensitive in
XML.
<li>
<p>In CSS3, <dfn id=identifiers title=identifier>identifiers</dfn>
(including element names, classes, and IDs in selectors (see <a
href="#SELECT" rel=biblioentry>[SELECT]<!--{{!SELECT}}--></a> <span
class=issue>[or is this still true]</span>)) can contain only the
characters [A-Za-z0-9] and ISO 10646 characters 161 and higher, plus the
hyphen (-) and the underscore (_); they cannot start with a digit or a
hyphen followed by a digit. They can also contain escaped characters and
any ISO 10646 character as a numeric code (see next item). <span
class=example>For instance, the identifier "<code>B&W?</code>" may
be written as "<code>B\&W\?</code>" or "<code>B\26
W\3F</code>".</span> (See <a href="#UNICODE310"
rel=biblioentry>[UNICODE310]<!--{{!UNICODE310}}--></a> and <a
href="#ISO10646" rel=biblioentry>[ISO10646]<!--{{!ISO10646}}--></a>.)
<li>
<p>In CSS3, a backslash (\) character indicates three types of <dfn
id=character-escapes title="backslash escapes">character escapes</dfn>.</p>
<p>First, inside a string (see <a href="#CSS3VAL"
rel=biblioentry>[CSS3VAL]<!--{{!CSS3VAL}}--></a>), a backslash followed
by a newline is ignored (i.e., the string is deemed not to contain
either the backslash or the newline).</p>
<p>Second, it cancels the meaning of special CSS characters. Any
character (except a hexadecimal digit) can be escaped with a backslash
to remove its special meaning. For example, <samp>"\""</samp> is a
string consisting of one double quote. Style sheet preprocessors must
not remove these backslashes from a style sheet since that would change
the style sheet's meaning.</p>
<p>Third, backslash escapes allow authors to refer to characters they
can't easily put in a style sheet. In this case, the backslash is
followed by at most six hexadecimal digits (0..9A..F), which stand for
the ISO 10646 (<a href="#ISO10646"
rel=biblioentry>[ISO10646]<!--{{!ISO10646}}--></a>) character with that
number. If a digit or letter follows the hexadecimal number, the end of
the number needs to be made clear. There are two ways to do that:</p>
<ol>
<li>with a space (or other whitespace character): "\26 B" ("&B"). In
this case, user agents should treat a "CR/LF" pair (13/10) as a single
whitespace character.
<li>by providing exactly 6 hexadecimal digits: "\000026B" ("&B")
</ol>
<p>In fact, these two methods may be combined. Only one whitespace
character is ignored after a hexadecimal escape. Note that this means
that a "real" space after the escape sequence must itself either be
escaped or doubled.</p>
<li>
<p>Backslash escapes are always considered to be part of an <a
href="#identifiers">identifier</a> or a string (i.e., "\7B" is not
punctuation, even though "{" is, and "\32" is allowed at the start of a
class name, even though "2" is not).
</ul>
<h3 id=tokenization><span class=secno>4.2. </span>Tokenization</h3>
<p class=issue>[This needs to be integrated with the selectors module. How
should that be done?]
<p>All levels of CSS — level 1, level 2, level 3, and any future
levels — use the same core syntax. This allows UAs to parse (though
not completely understand) style sheets written in levels of CSS that
didn't exist at the time the UAs were created. Designers can use this
feature to create style sheets that work with older user agents, while
also exercising the possibilities of the latest levels of CSS.
<p>At the lexical level, CSS style sheets consist of a sequence of tokens.
Hexadecimal codes (e.g., <code>#x20</code>) refer to ISO 10646 (<a
href="#ISO10646" rel=biblioentry>[ISO10646]<!--{{!ISO10646}}--></a>). In
case of multiple matches, the longest match determines the token.
<p>The following productions are <em>parts</em> of tokens:
<p class=issue>[We need something to allow signs on integers. Do we need to
go as far as css3-selectors?]
<table>
<tbody>
<tr>
<td id=SUBTOK-ident>ident
<td>::=
<td><code>'-'? <a href="#SUBTOK-nmstart">nmstart</a> <a
href="#SUBTOK-nmchar">nmchar</a>*</code>
<tr>
<td id=SUBTOK-name>name
<td>::=
<td><code><a href="#SUBTOK-nmchar">nmchar</a>+</code>
<tr>
<td id=SUBTOK-nmstart>nmstart
<td>::=
<td><code>[a-zA-Z] | '_' | <a href="#SUBTOK-nonascii">nonascii</a> | <a
href="#SUBTOK-escape">escape</a></code>
<tr>
<td id=SUBTOK-nonascii>nonascii
<td>::=
<td><code>[#x80-#xD7FF#xE000-#xFFFD#x10000-#x10FFFF]</code>
<tr>
<td id=SUBTOK-unicode>unicode
<td>::=
<td><code>'\' [0-9a-fA-F]{1,6} <a href="#SUBTOK-wc">wc</a>?</code>
<tr>
<td id=SUBTOK-escape>escape
<td>::=
<td><code><a href="#SUBTOK-unicode">unicode</a> | '\'
[#x20-#x7E#x80-#xD7FF#xE000-#xFFFD#x10000-#x10FFFF]</code>
<tr>
<td id=SUBTOK-nmchar>nmchar
<td>::=
<td><code>[a-zA-Z0-9] | '-' | '_' | <a
href="#SUBTOK-nonascii">nonascii</a> | <a
href="#SUBTOK-escape">escape</a></code>
<tr>
<td id=SUBTOK-num>num
<td>::=
<td><code>[0-9]+ | [0-9]* '.' [0-9]+</code>
<tr>
<td id=SUBTOK-string>string
<td>::=
<td><code>'"' (<a href="#SUBTOK-stringchar">stringchar</a> | "'")* '"' |
"'" (<a href="#SUBTOK-stringchar">stringchar</a> | '"')* "'"</code>
<tr>
<td id=SUBTOK-stringchar>stringchar
<td>::=
<td><code><a href="#SUBTOK-urlchar">urlchar</a> | #x20 | '\' <a
href="#SUBTOK-nl">nl</a></code>
<tr>
<td id=SUBTOK-urlchar>urlchar
<td>::=
<td><code>[#x9#x21#x23-#x26#x27-#x7E] | <a
href="#SUBTOK-nonascii">nonascii</a> | <a
href="#SUBTOK-escape">escape</a></code>
<tr>
<td id=SUBTOK-nl>nl
<td>::=
<td><code>#xA | #xD #xA | #xD | #xC</code>
<tr>
<td id=SUBTOK-w>w
<td>::=
<td><code><a href="#SUBTOK-wc">wc</a>*</code>
<tr>
<td id=SUBTOK-wc>wc
<td>::=
<td><code>#x9 | #xA | #xC | #xD | #x20</code>
</table>
<p>The following productions are the complete list of tokens in CSS3:
<table>
<tbody>
<tr>
<td id=TOK-IDENT>IDENT
<td>::=
<td><code><a href="#SUBTOK-ident">ident</a></code>
<tr>
<td id=TOK-ATKEYWORD>ATKEYWORD
<td>::=
<td><code>'@' <a href="#SUBTOK-ident">ident</a></code>
<tr>
<td id=TOK-STRING>STRING
<td>::=
<td><code><a href="#SUBTOK-string">string</a></code>
<tr>
<td id=TOK-HASH>HASH
<td>::=
<td><code>'#' <a href="#SUBTOK-name">name</a></code>
<tr>
<td id=TOK-NUMBER>NUMBER
<td>::=
<td><code><a href="#SUBTOK-num">num</a></code>
<tr>
<td id=TOK-PERCENTAGE>PERCENTAGE
<td>::=
<td><code><a href="#SUBTOK-num">num</a> '%'</code>
<tr>
<td id=TOK-DIMENSION>DIMENSION
<td>::=
<td><code><a href="#SUBTOK-num">num</a> <a
href="#SUBTOK-ident">ident</a></code>
<tr>
<td id=TOK-URI>URI
<td>::=
<td><code>"url(" <a href="#SUBTOK-w">w</a> (<a
href="#SUBTOK-string">string</a> | <a
href="#SUBTOK-urlchar">urlchar</a>* ) <a href="#SUBTOK-w">w</a>
")"</code>
<tr>
<td id=TOK-UNICODE-RANGE>UNICODE-RANGE
<td>::=
<td><code>"U+" [0-9A-F?]{1,6} ('-' [0-9A-F]{1,6})?</code>
<tr>
<td id=TOK-CDO>CDO
<td>::=
<td><code>"<!--"</code>
<tr>
<td id=TOK-CDC>CDC
<td>::=
<td><code>"-->"</code>
<tr>
<td id=TOK-S>S
<td>::=
<td><code><a href="#SUBTOK-wc">wc</a>+</code>
<tr>
<td id=TOK-COMMENT>COMMENT
<td>::=
<td><code>"/*" [^*]* '*'+ ([^/] [^*]* '*'+)* "/"</code>
<tr>
<td id=TOK-FUNCTION>FUNCTION
<td>::=
<td><code><a href="#SUBTOK-ident">ident</a> '('</code>
<tr>
<td id=TOK-INCLUDES>INCLUDES
<td>::=
<td><code>"~="</code>
<tr>
<td id=TOK-DASHMATCH>DASHMATCH
<td>::=
<td><code>"|="</code>
<tr>
<td id=TOK-PREFIXMATCH>PREFIXMATCH
<td>::=
<td><code>"^="</code>
<tr>
<td id=TOK-SUFFIXMATCH>SUFFIXMATCH
<td>::=
<td><code>"$="</code>
<tr>
<td id=TOK-SUBSTRINGMATCH>SUBSTRINGMATCH
<td>::=
<td><code>"*="</code>
<tr>
<td id=TOK-CHAR>CHAR
<td>::=
<td>any other character not matched by the above rules, except for
<code>"</code> or <code>'</code>
<tr>
<td id=TOK-BOM>BOM
<td>::=
<td><code>#xFEFF</code>
</table>
<p> Since any single character other than ‘<code class=css> or " that
cannot be part of a larger token is a single character token, there cannot
be errors in tokenization other than the inability to tokenize an
unmatched quotation mark. If at some point it is not possible to continue
tokenizing an incoming style sheet, the remainder of the style sheet
should be ignored and only the largest initial segment of the style sheet
that can be tokenized according to the above rules (that is, the entire
style sheet except for the part from the unmatched (single or double)
quotation mark to the end) should be used to form the sequence of tokens
to be parsed according to the grammar. </code>
<p class=issue>[This isn’t exactly right. Since the string token
can't contain newlines that aren't escaped by backslashes, an
untokenizable sequence can occur in the middle of a file. Would it be
better to change things so that unmatched quotation marks become
single-character tokens and all character streams are tokenizable?]
<h3 id=grammar><span class=secno>4.3. </span>Grammar</h3>
<h4 id=principles-of-css-error-handling><span class=secno>4.3.1.
</span>Principles of CSS error handling</h4>
<p>All levels of CSS, starting from CSS1, have required that user agents
ignore certain types of invalid style sheets in well-defined ways. This
allows forward-compatibility, since it allows future extensions to CSS
within basic grammatical constraints that will be ignored in well-defined
ways by user agents implementing earlier versions of CSS.
<p>Handling of CSS that is not valid CSS3 but is valid according to the
forward-compatible syntax requires first determining the beginning and end
of the part that is invalid and then handling that part in a specified
way. The latter is described in the <a href="#error-handling">rules for
handling parsing errors</a>. The mechanism for the former is described
within the grammar.
<p>The handling of style sheets that do not parse according to the
forward-compatible core syntax is not defined by this specification. <span
class=issue>[Should it be?]</span>
<p>Certain productions within the grammar are <dfn
id=error-handling-points>error handling points</dfn>. Every error handling
point has a backup production that is to be used if it is not possible to
parse the stream of tokens based on the primary production. If the error
handling production is represented as <code>prod</code>, then the backup
production is represented as <code>FAIL(prod)</code>.
<p class=issue>[The <a href="#detailed-grammar">grammar</a> given in
Appendix D of CSS2 still needs to be incorporated into this specification.
The editor hopes that it can be done by unifying it with the
forward-compatible grammar into a single grammar that describes both the
rules for forward-compatible parsing and the syntax of what is currently
possible in CSS, but that may not be possible. However, hopefully it will
be possible to do this by describing the general grammar in terms of the
concepts described in the previous paragraph.]
<p>Excluding the transformation of a production into its backup production,
this grammar is LL(1). <span class=issue>[We should explain briefly what
this means, except that it's probably not true. It's probably just
LALR(1).]</span>
<p>The portion of a CSS style sheet that is to be used is the largest
initial stream of the tokens resulting from the <a
href="#tokenization">tokenization process</a> that can be parsed according
to the grammar presented in this chapter. (For example, if a brace closing
a declaration block <span class=issue>[link-ify this]</span> is not
present, the declaration block must be ignored since the closing brace is
required to satisfy this grammar.) <span class=issue>[This might lead to
highly unexpected behavior when there's an extra closing brace (etc.). Do
we really want this?]</span>
<p>Some of the constraints of CSS are not expressed in the grammar. For
example, an <a href="#charset0"><code>@charset</code></a> rule is not
permitted in an embedded style sheet, or a namespace prefix that has not
been defined by an <code>@namespace</code> rule is an invalid selector.
These constraints should be handled just as a parsing error would be (by
ignoring out to the next backup production) unless specified otherwise.
<h4 id=style-sheets><span class=secno>4.3.2. </span>Style sheets</h4>
<p>Below is the core syntax for CSS. Lowercase identifiers represent
productions in this grammar, uppercase identifiers represent tokens (see
above), and characters in single quotes (‘<code class=css>)
represent CHAR tokens (see above). The sections that follow describe how
to use it.</code>
<p class=issue>[This might need better integration with the selectors
module, although maybe it’s ok.]
<pre>
stylesheet : [ CDO | CDC | S | statement ]*;
statement : ruleset | at-rule;
at-rule : ATKEYWORD S* any* [ block | ';' S* ];
block : '{' S* [ any | block | ATKEYWORD S* | ';' S* ]* '}' S*;
ruleset : selector? '{' S* declaration? [ ';' S* declaration? ]* '}' S*;
selector : any+;
declaration : property ':' S* value;
property : IDENT S*;
value : [ any | block | ATKEYWORD S* ]+;
any : [ IDENT | NUMBER | PERCENTAGE | DIMENSION | STRING
| DELIM | URI | HASH | UNICODE-RANGE | INCLUDES
| FUNCTION S* any* ')' | DASHMATCH | '(' S* any* ')'
| '[' S* any* ']' ] S*;
</pre>
<div class=issue> [The definitions of these productions should be spread
below into the prose describing what they mean. Furthermore, they should
be combined with the Appendix D grammar from CSS2, perhaps using notation
like:
<table>
<tbody>
<tr>
<td>ruleset
<td>::=
<td>...
<tr>
<td>FAIL(ruleset)
<td>::=
<td>...
</table>
]</div>
<p><dfn id=comment>COMMENT</dfn> tokens do not occur in the grammar (to
keep it readable), but any number of these tokens may appear anywhere
between other tokens.
<p>The token S in the grammar above stands for <dfn