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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN">
<!--
ISSUES
- This list is not complete
- The specification is pretty vague and more importantly inconsistent about
liveness
-->
<html lang="en-US">
<head>
<title>Cascading Style Sheets Object Model (CSSOM)</title>
<style type="text/css">
pre.idl { border:solid thin; background:#eee; color:#000; padding:0.5em }
pre.idl :link, pre.idl :visited { color:inherit; background:transparent }
dfn { font-weight:bold; font-style:normal }
div.example { margin-left:1em; padding-left:1em; border-left:double; color:#222; background:#fcfcfc }
div.example table code { color:inherit }
td, th { padding:.1em }
.proposal { padding:.5em; border:solid blue }
p.note { margin-left:2em; color:green; font-style:italic; font-weight:bold }
p.note::before { content:"Note: " }
.issue { padding:.5em; border:solid red }
.issue::before { content:"Issue: " }
em.ct { text-transform:lowercase; font-variant:small-caps; font-style:normal }
code { color:orangered }
code :link, code :visited { color:inherit }
.members dt { margin:.5em 0 }
.members dd p:first-child { margin-top:0 }
.members dd p:last-child { margin-bottom:0 }
</style>
<link rel="stylesheet" href="http://www.w3.org/StyleSheets/TR/base">
</head>
<body class="draft">
<div class="head">
<h1 id="cssom">Cascading Style Sheets Object Model (<abbr>CSSOM</abbr>)</h1>
<h2 class="no-num no-toc" id="">Editor's draft <!--W3C Working Draft--> [DATE: 3 August 2002]</h2>
<dl>
<dt>This version:</dt>
<dd><a href="[VERSION]">http://www.w3.org/TR/[YEAR]/WD-cssom-[CDATE]/</a></dd>
<dt>Latest version:</dt>
<dd><a href="http://www.w3.org/TR/cssom/">http://www.w3.org/TR/cssom/</a></dd>
<dt>Previous versions:</dt>
<dd><a href="http://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113/">http://www.w3.org/TR/2000/REC-DOM-Level-2-Style-20001113/</a></dd>
<dt>Editor:</dt>
<dd><a href="http://annevankesteren.nl/">Anne van Kesteren</a>
(<a href="http://www.opera.com/">Opera Software ASA</a>)
<<a href="mailto:annevk@opera.com">annevk@opera.com</a>></dd>
</dl>
</div>
<h2 class="no-num no-toc" id="abstract">Abstract</h2>
<p>The Cascading Style Sheets Object Model defines enables developers to find
style sheets associated with a <code>Document</code>, to query and modify
rules within a CSS style sheet (through an object model) and to find out
layout related information from objects within a <code>Document</code>.</p>
<h2 class="no-num no-toc" id="sotd">Status of this Document</h2>
<p class="issue">This document is in its very early stages. The intention is
that this specification will in due course supercede DOM Level 2 Style.</p>
<h2 class="no-num no-toc" id="toc">Table of Contents</h2>
<!--toc-->
<h2 id="introduction">Introduction</h2>
<p class="issue">...</p>
<h3 id="history">History</h3>
<p><em>This section is non normative.</em></p>
<p>Several interfaces from DOM Level 2 Style <a
href="http://www.w3.org/mid/Pine.LNX.4.05.10310302134070.1173-100000@lanalana.inria.fr"
title="[CSSOM] CSSValue and related interfaces (message from the CSS WG)">have
been obsoleted</a> because they where thought to be too akward for frequent
use. This specification no longer contains those features.</p>
<p>In addition, <code>DOMImplementationCSS</code> has been removed as well,
because there was no use case provided in DOM Level 2 Style.</p>
<h3 id="conformance">Conformance Requirements</h3>
<p>Everything in this specification is normative except for diagrams,
examples, notes and sections marked non-normative.</p>
<p>The key words <em class="ct">must</em>, <em class="ct">must not</em>,
<em class="ct">required</em>, <em class="ct">shall</em>, <em class="ct">shall
not</em>, <em class="ct">should</em>, <em class="ct">should not</em>,
<em class="ct">recommended</em>, <em class="ct">may</em>, and
<em class="ct">optional</em> in the normative parts of this document are to be
interpreted as described in
[<cite><a href="#ref-rfc2119">RFC2119</a></cite>].</p>
<p>The following conformance classes are defined (and considered) by this
specification:</p>
<dl>
<dt><dfn id="conforming-implementation">conforming implementation</dfn></dt>
<dd>A user agent that implements all interfaces described in this
specification and follows all <em class="ct">must</em>-,
<em class="ct">required</em>- and <em class="ct">shall</em>-level of critera
in this specification.</dd>
<dt><dfn id="conforming document">conforming document</dfn></dt>
<dd>A document that follows all <em class="ct">must</em>-,
<em class="ct">required</em>- and <em class="ct">shall</em>-level of critera
in this specification that apply to document authors.</dd>
<dt><dfn id="conforming-authoring-tool">conforming authoring tool</dfn></dt>
<dd>One that produces conforming documents.</dd>
</dl>
<h4 id="terminology">Terminology and Conventions</h4>
<p>A <dfn>color component integer</dfn> is a base-ten integer in the range
0-255 using digits 0-9, U+0030 to U+0039, in the shortest form possible.</p>
<p>A <dfn>color component separator</dfn> is a literal U+002C COMMA followed
by a U+0020 SPACE.</p>
<p>When this specification talks about object <code><var>A</var></code>
where <code><var>A</var></code> is actually an interface, it generally means
an object implementing interface <code><var>A</var></code>.</p>
<!--
<p>The term <dfn id="whitespace">whitespace</dfn> when used in this
specification refers to the U+0020 SPACE, U+0009 <control>, U+000A
<control>, U+000D <control> and U+000C <control> (if
applicable).</p>
-->
<p>The terms <dfn id="whitespace">whitespace</dfn> and
<dfn id="style-sheet">style sheet</dfn> are used as defined in the <cite>CSS
2.1 Specification</cite> [CSS21].</p>
<p>A <dfn id="css-style-sheet">CSS style sheet</dfn> is a <span>style
sheet</span> that conforms to the CSS syntax rules.</p>
<!-- XXX: "Cascading Style Sheet style sheet" is just a joke... -->
<h4>DOM feature strings</h4>
<!-- Thanks to Hixie. This is from HTML5. -->
<p>DOM Level 3 Core defines mechanisms for checking for interface support,
and for obtaining implementations of interfaces, using <a
href="http://www.w3.org/TR/DOM-Level-3-Core/core.html#DOMFeatures">feature
strings</a>. <a>[DOM3CORE]</a></p>
<p>A DOM application can use the <code>hasFeature(<var title="">feature</var>,
<var title="">version</var>)</code> method of the
<code>DOMImplementation</code> interface with parameter values
"<code title="">StyleSheets</code>" and "<code>3.0</code>" (respectively)
to determine whether or not "Accessing style sheets through the DOM" is
supported by the implementation. The feature string
"<code title="">CSS</code>" (with version string "<code>3.0</code>") can
be used to check if the implementation supports "Cascading Style Sheets APIs"
and "<code title="">Layout</code>" (with version string "<code>3.0</code>")
can be used to check if the implementation supports "Layout APIs". User agents
<em class="ct">should</em> respond with a <code>true</code> value when the
<code>hasFeature</code> method is queried with these values. Authors are
cautioned, however, that user agents returning <code>true</code> might not be
perfectly compliant, and that user agents returning <code>false</code> might
well have support for features in this specification; in general, therefore,
use of this method is discouraged.</p>
<p>The values "<code title="">StyleSheets</code>", "<code title="">CSS</code>"
and "<code title="">Layout</code>" (all with version "<code>3.0</code>")
<em class="ct">should</em> also be supported in the context of the
<code>getFeature()</code> and <code>isSupported()</code> methods, as defined
by DOM Level 3 Core.</p>
<p class="note">The interfaces defined in this specification are not
always supersets of the interfaces defined in DOM Level 2 Style; some features
that were formerly deprecated, poorly supported, rarely used or considered
unnecessary have been removed. Therefore it is not guarenteed that an
implementation that supports "<code title="">CSS</code>" "<code>3.0</code>"
also supports "<code title="">CSS</code>" "<code>2.0</code>".</p>
<h2>Accessing style sheets through the DOM</h2>
<p>Each style sheet is represented by a <code>StyleSheet</code> object. These
objects can be accessed through the <code>LinkStyle</code> interface
implemented on individual <code>Node</code> objects or through the
<code>DocumentStyle</code> interface implemented on the <code>Document</code>
object. The <code>DocumentStyle</code> interface also provides an interface
for enabling alternate style sheets and manipulating style sheet sets.</p>
<h3>Terminology</h3>
<p>Each style sheet can have a title. A <span>style sheet</span> is said to
<dfn id="style-sheet-title" title="have a title">have a title</dfn> if the
<code>title</code> attribute on the <code>StyleSheet</code> object is neither
<code>null</code> nor the empty string.</p>
<p><dfn title="persistent style sheet">Persistent style sheets</dfn> are style
sheets <span title="have a title">without a title</span>.</p>
<p>One or more style sheets <span title="have a title">with the same
title</span> (case-sensitive) form a <dfn title="style sheet set">style sheet
set</dfn>.</p>
<h3>The <code>LinkStyle</code> Interface</h3>
<p>Nodes within the DOM causing the association of a style sheet
<em class="ct">must</em> implement the <code>LinkStyle</code> interface.</p>
<pre class="idl">interface <dfn>LinkStyle</dfn> {
readonly attribute <span>StyleSheet</span> <span title="linkstyle-sheet">sheet</span>;
};</pre>
<dl class="members">
<dt><dfn id="linkstyle-sheet" title="linkstyle-sheet"><code>sheet</code></dfn>
of type <code>StyleSheet</code>, readonly</dt>
<dd>This attribute <em class="ct">must</em> be the <code>StyleSheet</code>
the node is referring to or <code>null</code> if the node is not referring to
a <code>StyleSheet</code> (for example, all <code>link</code> elements in
HTML implement this interface, but not all <code>link</code> elements are
used for style sheets).</dd>
</dl>
<p class="note">Whether or not the node refers to a style sheet is defined by
the specification the defines the semantics of said node.</p>
<h4>Requirements on specifications</h4>
<p>Specifications introducing new ways of associating style sheets through
the DOM <em class="ct">should</em> define which objects implement the
<code>LinkStyle</code> interface. In addition, these specifications
<em class="ct">should</em> define how these objects affect the potentially
associated <code>StyleSheet</code> object (when
<code title="linkstyle-sheet">sheet</code> is non-<code>null</code>).</p>
<h4>Requirements on specific user agents</h4>
<p>SVG user agents <em class="ct">must</em> implement <code>LinkStyle</code>
on objects implementing the <code>SVGStyleElement</code> interface. HTML user
agents <em class="ct">must</em> implement <code>LinkStyle</code> on objects
implementing <code>HTMLLinkElement</code> or <code>HTMLStyleElement</code>.
They <em class="ct">must</em> also implement it on objects implementing
<code>HTMLMetaElement</code> if the <code>Link</code> HTTP header is
supported.</p>
<p class="issue">Perhaps the above should be left to the HTML and SVG
specifications.</p>
<h4><code><?xml-stylesheet?></code> processing instruction</h4>
<p>User agents supporting supporting <code><?xml-stylesheet?></code>
<em class="ct">must</em> implement the <code>LinkStyle</code> on objects
implementing <code>ProcessingInstruction</code>.</p>
<p>If the <code title="">target</code> DOM attribute of the
<code>ProcessingInstruction</code> is not <code>xml-stylesheet</code> or if
the <code>href</code> pseudo-attribute of the processing instruction doesn't
point to an external resource or does point to an external resource that
has not yet been downloaded the <code title="linkstyle-sheet">sheet</code>
attribute <em class="ct">must</em> be <code>null</code>. Otherwise, if the
<code title="">target</code> DOM attribute is <code>xml-stylesheet</code>,
the resource has been downloaded and the determined type is a supported
style sheet language the <code title="linkstyle-sheet">sheet</code>
attribute <em class="ct">must</em> be a <code>StyleSheet</code> object with
the members implemented as follows:</p>
<dl>
<dt><code title="stylesheet-type">type</code></dt>
<dd>This <em class="ct">must</em> be the determined type.</dd>
<dt><code title="stylesheet-href">href</code></dt>
<dd>This <em class="ct">must</em> be the value of the <code>href</code>
pseudo-attribute.</dd>
<dt><code title="stylesheet-media">media</code></dt>
<dd>This <em class="ct">must</em> be the value of the <code>media</code>
pseudo-attribute.</dd>
<dt><code title="stylesheet-title">title</code></dt>
<dd>This <em class="ct">must</em> be the value of the <code>title</code>
pseudo-attribute.</dd>
</dl>
<h3>The <code>DocumentStyle</code> Interface</h3>
<p>Any object implementing the <code>Document</code> interface
<em class="ct">must</em> also implement the <code>DocumentStyle</code>
interface.</p>
<!-- https://bugzilla.mozilla.org/show_bug.cgi?id=200930 (FIXED) -->
<pre class="idl">interface <dfn>DocumentStyle</dfn> {
readonly attribute <span>StyleSheetList</span> <span>styleSheets</span>;
attribute DOMString <span>selectedStyleSheetSet</span>;
readonly attribute DOMString <span>lastStyleSheetSet</span>;
readonly attribute DOMString <span>preferredStyleSheetSet</span>;
readonly attribute DOMStringList <span>styleSheetSets</span>;
void <span title="documentstyle-enablestylesheetsforset">enableStylesheetsForSet</span>(in DOMString <var>name</var>);
};</pre>
<p>For this interface, the <code>DOMString</code> values <code>null</code> and
"the empty string" are distinct, and <em class="ct">must</em> not be
considered equivalent.</p>
<p>The members are defined as follows:</p>
<dl class="members">
<dt><dfn id="documentstyle-stylesheets"><code>styleSheets</code></dfn> of
type <code>StyleSheetList</code></dt>
<dd>
<p>This attribute <em class="ct">must</em> be a <code>StyleSheetList</code>
object containing a collection of all <code>LinkStyle</code> objects with a
non-<code>null</code> <code title="linkstyle-sheet">sheet</code> attribute
in document order preceeded by style sheets introduced through HTTP
headers.</p>
</dd>
<dt><dfn id="documentstyle-selectedStyleSheetSet"><code>selectedStyleSheetSet</code></dfn>
of type <code>DOMString</code></dt>
<dd>
<p>This attribute indicates which <span>style sheet set</span> is in use.
This attribute is <span>live</span>; changing the
<code title="stylesheet-disabled">disabled</code> attribute on style sheets
directly will change the value of this attribute.</p>
<p>If all the sheets that are enabled and <span>have a title</span> have the
<em>same</em> title (by <span>case-sensitive</span> comparisons) then the
value of this attribute <em class="ct">must</em> be exactly equal to the
title of the first enabled style sheet with a title in the
<code>styleSheets</code> list. Otherwise, if style sheets from different
sets are enabled, then the return value <em class="ct">must</em> be
<code>null</code> (there is no way to determine what the currently selected
style sheet set is in those conditions). Otherwise, either all style sheets
that <span>have a title</span> are disabled, or there are no alternate style
sheets, and <code>selectedStyleSheetSet</code> <em class="ct">must</em>
return the empty string.</p>
<p>Setting this attribute to the <code>null</code> value
<em class="ct">must</em> have no effect.</p>
<p>Setting this attribute to a non-<code>null</code> value
<em class="ct">must</em> call
<code title="documentstyle-enablestylesheetsforset">enableStylesheetsForSet()</code>
with that value as the method's argument, and set
<code>lastStyleSheetSet</code> to that value.</p>
<p>From the DOM's perspective, all views have the same
<code>selectedStyleSheetSet</code>. If a user agent supports multiple views
with different selected alternate style sheets, then this attribute (and the
<code>StyleSheet</code> interface's <code>disabled</code> attribute)
<em class="ct">must</em> return and set the value for the default view.</p>
</dd>
<dt><dfn id="documentstyle-lastStyleSheetSet"><code>lastStyleSheetSet</code></dfn>
of type <code>DOMString</code>, readonly</dt>
<dd>
<p>This property <em class="ct">must</em> initially have the value
<code>null</code>. Its value changes when the
<code>selectedStyleSheetSet</code> attribute is set.</p>
</dd>
<dt><dfn id="documentstyle-preferredStyleSheetSet"><code>preferredStyleSheetSet</code></dfn>
of type <code>DOMString</code>, readonly</dt>
<dd>
<p>This attribute <em class="ct">must</em> be the preferred style
sheet set as set by the author. It is determined from the order of
style sheet declarations and the <code>Default-Style</code> HTTP headers.
If there is no preferred style sheet set, this attribute
<em class="ct">must</em> be the empty string. The case of this attribute
<em class="ct">must</em> exactly match the case given by the author where
the preferred style sheet is specified or implied. This attribute
<em class="ct">must</em> never be <code>null</code>.</p>
</dd>
<dt><dfn id="documentstyle-styleSheetSets"><code>styleSheetSets</code></dfn>
of type <code>DOMStringList</code>, readonly</dt>
<dd>
<p>This <em class="ct">must</em> be a <span>live</span> list of the
currently available <span>style sheet sets</span>. This list is constructed
by enumerating all the style sheets for this document available to the
implementation, in the order they are listed in the <code>styleSheets</code>
attribute, adding the title of each style sheet
<span title="have a title">with a title</span> to the list, avoiding
duplicates by dropping titles that match (<span>case-sensitively</span>)
titles that have already been added to the list.</p>
</dd>
<dt><dfn id="documentstyle-enablestylesheetsforset" title="documentstyle-enablestylesheetsforset"><code>enableStylesheetsForSet(<var title="">name</var>)</code></dfn>,
method</dt>
<dd>
<p>Invoking this method <em class="ct">must</em> change the
<code title="stylesheet-disabled">disabled</code> attribute on each
<code>StyleSheet</code> object
<span title="have a title">with a title</span> in the
<code>styleSheets</code> attribute, so that all those whose title matches
the <var title="">name</var> argument are enabled, and all others are
disabled. Title matches <em class="ct">must</em> be
<span>case-sensitive</span>.</p>
<p>Invoking this method with the empty string value <em class="ct">must</em>
disable all alternate and preferred style sheets (but does not change the
state of persistent style sheets).</p>
<p>Invoking this method with the <code>null</code> value
<em class="ct">must</em> have no effect.</p>
<!-- fact: -->
<p>Style sheets that do not <span>have a title</span> are never affected by
this method. This method does not change the values of the
<code>lastStyleSheetSet</code> or <code>preferredStyleSheetSet</code>
attributes.</p>
</dd>
</dl>
<h3>The <code>StyleSheetList</code> Interface</h3>
<p>The object implementing this interface represents a live collection of
<code>StyleSheet</code> objects.</p>
<p>In bindings that allow it, enumerating a <code>StyleSheetList</code> object
<em class="ct">must</em> enumerate through the currently stored and
accessible items in the list the object is associated with. This ensures
<code>document.styleSheets[1].<var>x</var></code> is possible from ECMAScript
for example.</p>
<pre class="idl">interface <dfn>StyleSheetList</dfn> {
readonly attribute unsigned long <span title="stylesheetlist-length">length</span>;
<span>StyleSheet</span> <span title="stylesheetlist-item">item</span>(in unsigned long <var title="">index</var>);
};</pre>
<p>The members of the <code>StyleSheetList</code> object are defined as
follows:</p>
<dl class="members">
<dt><dfn id="stylesheetlist-length" title="stylesheetlist-length"><code>length</code></dfn>,
of type <code>unsigned long</code>, readonly</dt>
<dd>This attribute <em class="ct">must</em> be the number of
<code>StyleSheet</code> objects currently in the list.</dd>
<dt><dfn id="stylesheetlist-item" title="stylesheetlist-item"><code>item(<var title="">index</var>)</code></dfn>,
method</dt>
<dd>When invoked, this method <em class="ct">must</em> return the
<code>StyleSheet</code> in the list given by <var>index</var>. If
<var>index</var> is less than zero then this method <em class="ct">must</em>
raise an <code>INDEX_SIZE_ERR</code> exception. If <var>index</var> is
greater than or equal to the number of style sheets currently in the list
this method <em class="ct">must</em> return <code>null</code>.</dd>
<!-- Internet Explorer throws an exception for [largevalue] as well. -->
</dl>
<h3>Dynamically adding new style sheets</h3>
<p>If new style sheets <span title="have a title">with titles</span> are added
to the document, the user agent <em class="ct">must</em> decide whether or not
the style sheets should be initially enabled or not. How this happens depends
on the exact state of the document at the time the style sheet is added, as
follows.</p>
<h4>Adding style sheets</h4>
<p>First, if the style sheet is a preferred style sheet (it
<span title="have a title">has a title</span>, but is not marked as
alternate), and there is no
current preferred style sheet (the <code>preferredStyleSheetSet</code>
attribute is equal to the empty string) then the
<code>preferredStyleSheetSet</code> attribute is set to the exact value of
this style sheet's title. (This changes the preferred style sheet set, which
causes further changes — see below.)</p>
<p>Then, for all sheets, if any of the following is true, then the style sheet
<em class="ct">must</em> be enabled:</p>
<ul>
<li>The style sheet has an empty title.</li>
<li>The <code>lastStyleSheetSet</code> is <code>null</code>, and the style
sheet's title matches (by <span>case-sensitive</span> match) the value of
the <code>preferredStyleSheetSet</code> attribute.</li>
<li>The style sheet's title matches (by <span>case-sensitive</span> match)
the value of the <code>lastStyleSheetSet</code> attribute.</li>
</ul>
<p>Otherwise, the style sheet <em class="ct">must</em> be disabled.</p>
<h4>Changing the preferred style sheet set</h4>
<p>The first time the <span>preferred style sheet</span> set is set, which is
either before any alternate style sheets are seen (e.g. using a
<code>Default-Style</code> HTTP header), or is the first time a titled,
non-alternate style sheet is seen (in the absence of information to
the contrary, the first titled non-alternate sheet sets the name of
the preferred set), the <code>preferredStyleSheetSet</code> attribute's value
<em class="ct">must</em> be set to the name of that preferred style sheet
set. This does not change the <code>lastStyleSheetSet</code> attribute.</p>
<p>If the user agent has the preferred style sheet set changed, for example
if it receives a <code>Default-Style</code> HTTP header after it receives HTTP
<code>Link</code> headers implying another preferred style sheet, then the
<code>preferredStyleSheetSet</code> attribute's value
<em class="ct">must</em> be changed appropriately, and, if the
<code>lastStyleSheetSet</code> is <code>null</code>, the
<code title="documentstyle-enablestylesheetsforset">enableStylesheetsForSet()</code>
method <em class="ct">must</em> be called with the new
<code>preferredStyleSheetSet</code> value. (The
<code>lastStyleSheetSet</code> attribute is, again, not changed.)</p>
<h4>Examples</h4>
<div class="example">
<p>Thus, in the following HTML snippet:</p>
<pre><link rel="alternate stylesheet" title="foo" href="a">
<link rel="alternate stylesheet" title="bar" href="b">
<script>
document.selectedStyleSheetSet = 'foo';
document.styleSheets[1].disabled = false;
</script>
<link rel="alternate stylesheet" title="foo" href="c">
<link rel="alternate stylesheet" title="bar" href="d"></pre>
<p>...the style sheets that end up enabled are style sheets "a", "b",
and "c", the <code>selectedStyleSheetSet</code> attribute would
return null, <code>lastStyleSheetSet</code> would return "foo", and
<code>preferredStyleSheetSet</code> would return "".</p>
<p>Similarly, in the following HTML snippet:</p>
<pre><link rel="alternate stylesheet" title="foo" href="a">
<link rel="alternate stylesheet" title="bar" href="b">
<script>
var before = document.preferredStyleSheetSet;
document.styleSheets[1].disabled = false;
</script>
<link rel="stylesheet" title="foo" href="c">
<link rel="alternate stylesheet" title="bar" href="d">
<script>
var after = document.preferredStyleSheetSet;
</script></pre>
<p>...the "before" variable will be equal to the empty string, the
"after" variable will be equal to "foo", and style sheets "a" and "c"
will be enabled. This is the case even though the first script block
sets style sheet "b" to be enabled, because upon parsing the
following <code><link></code> element, the
<code>preferredStyleSheetSet</code> is set and the
<code title="documentstyle-enablestylesheetsforset">enableStylesheetsForSet()</code>
method is called (since <code>selectedStyleSheetSet</code> was never set
explicitly, leaving <code>lastStyleSheetSet</code> at <code>null</code>
throughout), which changes which style sheets are enabled and which are
not.</p>
</div>
<h3>Interaction with the User Interface</h3>
<p>The user interface of Web browsers that support style sheets
<em class="ct">should</em> list the style sheet titles given in the
<code>styleSheetSets</code> list, showing the
<code>selectedStyleSheetSet</code> as the selected style sheet set,
leaving none selected if it is <code>null</code> or the empty string, and
selecting an extra option "Basic Page Style" (or similar) if it is
the empty string and the <code>preferredStyleSheetSet</code> is the
empty string as well.</p>
<p>Selecting a style sheet from this list should set the
<code>selectedStyleSheetSet</code> attribute. This (by definition)
affects the <code>lastStyleSheetSet</code> attribute.</p>
<h4>Persisting the selected style sheet set</h4>
<p>If UAs persist the selected style sheet set, they should use the
value of the <code>selectedStyleSheetSet</code> attribute, or if
that is <code>null</code>, the <code>lastStyleSheetSet</code> attribute, when
leaving the page (or at some other time) to determine the set name
to store. If that is <code>null</code> then the style sheet set should not be
persisted.</p>
<p>When re-setting the style sheet set to the persisted value (which can
happen at any time, typically at the first time the style sheets are
needed for styling the document, after the <code><head></code> of the document has
been parsed, after any scripts that are not dependent on computed
style have executed), the style sheet set should be set by setting the
<code>selectedStyleSheetSet</code> attribute as if the user had selected the set
manually.</p>
<p class="note">This specification does not give any suggestions on
how UAs should decide to persist the style sheet set or whether or
how to persist the selected set across pages.</p>
<h3>Forward compatibility</h3>
<p>Future versions of CSS may introduce ways of having alternate style sheets
declared at levels lower than the top level, i.e. embedded within other style
sheets. Implementations of this specification that also support this proposed
declaration of alternate style sheets are expected to perform depth-first
traversals of the <code>styleSheets</code> list, not simply enumerations of
the <code>styleSheets</code> list that only contains the top level.</p>
<p class="issue">Would that actually work?!</p>
<h3>The <code>StyleSheet</code> Interface</h3>
<p>Each style sheet is represented by a <code>StyleSheet</code> object.</p>
<pre class="idl">interface <dfn>StyleSheet</dfn> {
readonly attribute DOMString <span title="stylesheet-type">type</span>;
attribute boolean <span title="stylesheet-disabled">disabled</span>;
readonly attribute Node <span title="stylesheet-ownernode">ownerNode</span>;
readonly attribute <span>StyleSheet</span> <span title="stylesheet-parentstylesheet">parentStyleSheet</span>;
readonly attribute DOMString <span title="stylesheet-href">href</span>;
readonly attribute DOMString <span title="stylesheet-title">title</span>;
readonly attribute <span>MediaList</span> <span title="stylesheet-media">media</span>;
};</pre>
<dl class="members">
<dt><dfn id="stylesheet-type" title="stylesheet-type"><code>type</code></dfn>
of type <code>DOMString</code>, readonly</dt>
<dd>
<p>This attribute indicates the MIME type of the style sheet. It's set by
objects which cause a <code>StyleSheet</code> object to be created, such
as <code>LinkStyle</code>.</p>
</dd>
<dt><dfn id="stylesheet-disabled" title="stylesheet-disabled"><code>disabled</code></dfn>
of type <code>boolean</code></dt>
<dd>
<p>On getting, this attribute <em class="ct">must</em> be <code>true</code>
when the style sheet is disabled and <code>false</code> otherwise.</p>
<p>On setting, a value of <code>true</code> <em class="ct">must</em> disable
the style sheet and a value of <code>false</code> enable it.</p>
</dd>
<dt><dfn id="stylesheet-ownernode" title="stylesheet-ownernode"><code>ownerNode</code></dfn>
of type <code>Node</code>, readonly</dt>
<dd>This attribute <em class="ct">must</em> be the <code>Node</code> that
associates the style sheet with the document or <code>null</code>
otherwise. This <code>Node</code> has implemented the
<code>LinkStyle</code> interface.</dd>
<dt><dfn id="stylesheet-parentstylesheet" title="stylesheet-parentstylesheet"><code>parentStyleSheet</code></dfn>
of type <code>StyleSheet</code>, readonly</dt>
<dd>This attribute <em class="ct">must</em> be the <code>StyleSheet</code>
object that caused the inclusion of the current style sheet or
<code>null</code> if there is no such object.</dd>
<dt><dfn id="stylesheet-href" title="stylesheet-href"><code>href</code></dfn>
of type <code>DOMString</code>, readonly</dt>
<dd>This attribute <em class="ct">must</em> be an IRI pointing to the
location of the standalone style sheet or <code>null</code> otherwise (when
it's inside a <code>style</code> element for example).</dd>
<!-- XXX: ready for IRI-hell? -->
<dt><dfn id="stylesheet-title" title="stylesheet-title"><code>title</code></dfn>
of type <code>DOMString</code></dt>
<dd>This attribute <em class="ct">must</em> be the
<span title="have a title">title</span> of the style sheet. In HTML this can
obtained from the <code>HTMLLinkElement</code> or
<code>HTMLStyleElement</code> for example.</dd>
<dt><dfn id="stylesheet-media" title="stylesheet-media"><code>media</code></dfn>
of type <code>MediaList</code>, readonly</dt>
<dd>
<p>This attribute <em class="ct">must</em> be a <code>MediaList</code>
object.</p>
<p>In binding languages that support setting to a readonly attribute setting
<code title="stylesheet-media">media</code> to a string
<em class="ct">must</em> set the value of
<code title="medialist-mediatext">mediaText</code> on the
<code>MediaList</code> object.</p>
<!-- XXX -->
</dd>
</dl>
<h3>The <code>MediaList</code> Interface</h3>
<p class="issue">This interface depends on the Media Queries specification
which still has some issues.</p>
<p>The <code>MediaList</code> object represents a collection of media
queries. It provides various ways to manipulate this collection.</p>
<p>In bindings that allow it, enumerating a <code>MediaList</code> object
<em class="ct">must</em> enumerate through the current collection of media
queries.</p>
<!--
<p>The items in the <code>MediaList</code> <em class="ct">must</em> be
accessible via an integral index, starting from 0.</p>
-->
<p>In bindings that allow it, such as ECMAScript, <code>MediaList</code>
objects <em class="ct">must</em> stringify to their
<code title="medialist-mediatext">mediaText</code> attribute's value.</p>
<pre class="idl">interface <dfn>MediaList</dfn> {
attribute DOMString <span title="medialist-mediatext">mediaText</span>;
readonly attribute unsigned long <span title="medialist-length">length</span>;
DOMString <span title="medialist-item">item</span>(in unsigned long <var title="">index</var>);
void <span title="medialist-appendmedium">appendMedium</span>(in DOMString <var title="">medium</var>)
void <span title="medialist-deletemedium">deleteMedium</span>(in DOMString <var title="">medium</var>)
};</pre>
<dl class="members">
<dt><dfn id="medialist-mediatext" title="medialist-mediatext"><code>mediaText</code></dfn>
of type <code>DOMString</code></dt>
<dd>
<p>On getting this attribute <em class="ct">must</em> be a comma-separated
list of <span title="canon-media">normalized media queries</span> or the
empty string otherwise.</p>
<p>On setting <span class="issue">...</span>.</p>
<!-- XXX Media Queries need to define parsing of media queries more
accurately. -->
</dd>
<dt><dfn id="medialist-length" title="medialist-length"><code>length</code></dfn>
of type <code>unsigned long</code></dt>
<dd>This attribute <em class="ct">must</em> be the number of media in the
list.</dd>
<dt><dfn id="medialist-item" title="medialist-item"><code>item(<var title="">index</var>)</code></dfn>,
method</dt>
<dd>When invoked, this method <em class="ct">must</em> return the media
query in the collection given by <var>index</var>. If <var>index</var> is
less than zero then this method <em class="ct">must</em> raise an
<code>INDEX_SIZE_ERR</code> exception. If <var>index</var> is greater than or
equal to the number of media queries currently in the collection this method
<em class="ct">must</em> return <code>null</code>.</dd>
<dt><dfn id="medialist-appendmedium" title="medialist-appendmedium"><code>appendMedium(<var title="">medium</var>)</code></dfn>,
method</dt>
<dd>When invoked, <span class="issue">...</span>.
<!--
XXX see above, Media Queries need to define parsing of media queries.
otherwise it <em class="ct">must</em> act as if
<code>deleteMedium</code> was invoked with <var>newMedium</var> as argument
(if it was in the list) and add <var>newMedium</var> to the end of the
list.
--></dd>
<dt><dfn id="medialist-deletemedium" title="medialist-deletemedium"><code>deleteMedium(<var title="">medium</var>)</code></dfn>,
method</dt>
<dd>This method, when invoked, <em class="ct">must</em> raise a
<code>NOT_FOUND_ERR</code> exception when <var>medium</var> is not in the
collection. Otherwise, <var>medium</var> <em class="ct">must</em> be removed
from the collection.</dd>
</dl>
<h2>Cascading Style Sheets APIs</h2>
<p><em>This section (and its subsections) are only applicable to user agents
implementing CSS.</em></p>
<p>The previous section provided a way of getting access to style sheets in a
generic way. This section provides a way for getting access to the individual
style rules within a Cascading Style Sheet as defined by the CSS
specifications. [CSS21]</p>
<h3>Processing CSS Statements</h3>
<p>The rules for <dfn title="insert a statement">inserting a statement</dfn>
are as given in the following algorithm. The variables <var>rule</var>,
<var>rule list</var> and <var>index</var> are to be considered equivalent to
the identically named variables used when invoking this algorithm. If an
exception is raised the algorithm is to be aborted. The steps
<em class="ct">must</em> be followed in order, as follows:</p>
<ol>
<li>If <var>index</var> is negative or greater than the length of the
<var>rule list</var> an <code>INDEX_SIZE_ERR</code> exception
<em class="ct">must</em> be raised.</li>
<li>Parse <var>rule</var> as a CSS statement. If the <var>rule</var> is
ignored by the CSS parser abort this algorithm (don't raise an exception).
Otherwise, create an object that implements one of the inherited interfaces
of <code>CSSStyle</code> appropriate for the parsed <var>rule</var>. Let
<var>object</var> be the newly created object.</li>
<li>If <var>object</var> can't be inserted within the <var>rule list</var>
at the given <var>index</var> because that's not allowed per the CSS
specification a <code>HIERARCHY_REQUEST_ERR</code> exception
<em class="ct">must</em> be raised.</li>
<li>Insert <var>object</var> at the given <var>index</var> within the
<var>rule list</var>.</li>
</ol>
<p>The rules for <dfn title="remove a statement">removing a statement</dfn>
are as given in the following algorithm. The variables <var>index</var> and
<var>rule list</var> are to be considered equivalent to the identically
named variables used when invoking this algorithm. If an exception is raised
this algorithm is to be aborted. The steps <em class="ct">must</em> be
followed in order, as follows:</p>
<ol>
<li>If <var>index</var> is negative or greater than the length of the
<var>rule list</var> an <code>INDEX_SIZE_ERR</code> exception
<em class="ct">must</em> be raised.</li>
<li>Remove the object at <var>index</var> from <var>rule list</var>.</li>
</ol>
<p>The rules for <dfn title="replace a statement">replacing a
statement</dfn> are as given in the following algorithm. The variable
<var>rule</var> and <var>old object</var> are to be considered equivalent to
the identically named variables used when invoking this algorithm. If an
exception is raised this algorithm is to be aborted. The steps
<em class="ct">must</em> be followed in order, as follows:</p>
<ol>
<li>Parse <var>rule</var> as a CSS statement. If the <var>rule</var> is
ignored by the CSS parser abort this algorithm (don't raise an exception).
Otherwise, create an object that implements one of the inherited interfaces
of <code>CSSStyle</code> appropriate for the parsed <var>rule</var>. Let
<var>object</var> be the newly created object.</li>
<li>If the <code title="cssrule-type">type</code> of new <var>object</var>
doesn't match the <code title="cssrule-type">type</code> of the object it
will replace raise an <code>INVALID_MODIFICATION_ERR</code> exception.</li>
<li>Replace <var>old object</var> with <var>object</var>.</li>
</ol>
<!-- XXX we should probably also detail how a CSSStyleRule is properly done
et cetera. -->
<h3>The <code>CSSStyleSheet</code> Interface</h3>
<p>The <code>CSSStyleSheet</code> interface represents a <span>CSS style
sheet</span>.</p>
<!--
IE exposes:
owningElement
pages
id
type
href
disabled
cssText
readOnly
title
parentStyleSheet
imports
rules
media
-->
<pre class="idl">interface <dfn>CSSStyleSheet</dfn> : <span>StyleSheet</span> {
readonly attribute <span>CSSRule</span> <span>ownerRule</span>;
readonly attribute <span>CSSRuleList</span> <span title="cssstylesheet-cssrules">cssRules</span>;
unsigned long <span title="cssstylesheet-insertrule">insertRule</span>(in DOMString <var>rule</var>, in unsigned long <var>index</var>);
void <span title="cssstylesheet-deleterule">deleteRule</span>(in unsigned long <var>index</var>);
};</pre>
<dl class="members">
<dt><dfn id="cssstylesheet-ownerrule"><code>ownerRule</code></dfn> of type
<code>CSSRule</code>, readonly</dt>
<dd>If the style sheet was loaded due to an <code>@import</code> rule this
attribute <em class="ct">must</em> be the <code>CSSImportRule</code> that
caused this style sheet to be imported. Otherwise it <em class="ct">must</em>
be <code>null</code>.</dd>
<dt><dfn id="cssstylesheet-cssrules" title="cssstylesheet-cssrules"><code>cssRules</code></dfn>
of type <code>CSSRuleList</code>, readonly</dt>
<dd>This attribute <em class="ct">must</em> be a live
<code>CSSRuleList</code> consisting of an ordered list of statements
(statements are either rulesets or at-rules).</dd>
<dt><dfn id="cssstylesheet-insertrule" title="cssstylesheet-insertrule"><code>insertRule(<var title="">rule</var>,
<var title="">index</var>)</code></dfn>, method</dt>
<dd>When invoked, user agents <em class="ct">must</em> <span>insert a
statement</span> where <var>rule</var> is <var>rule</var>, <var>index</var>
is <var>index</var> and <var>rule list</var> is
<code title="cssstylesheet-cssrules">cssRules</code>.
</dd>
<dt><dfn id="cssstylesheet-deleterule" title="cssstylesheet-deleterule"><code>deleteRule(<var title="">index</var>)</code></dfn>,
method</dt>
<dd>When invoked, user agents <em class="ct">must</em> <span>remove a
statement</span> where <var>index</var> is <var>index</var> and <var>rule
list</var> is
<code title="cssmediarule-cssrules">cssRules</code>.</dd>
</dl>
<h3>The <code>CSSRuleList</code> Interface</h3>
<p>The <code>CSSRuleList</code> interface represents an ordered list of
statements.</p>
<p>In bindings that allow it, enumerating a <code>CSSRuleList</code> object
<em class="ct">must</em> enumerate through the currently stored items in the
list the object is associated with.</p>
<pre class="idl">interface <dfn>CSSRuleList</dfn> {
readonly attribute unsigned long <span title="cssrulelist-length">length</span>;
<span>CSSRule</span> <span title="cssrulelist-item">item</span>(in unsigned long <var title="">index</var>);
};</pre>
<dl class="members">
<dt><dfn id="cssrulelist-length" title="cssrulelist-length"><code>length</code></dfn>
of type <code>unsigned long</code>, readonly</dt>
<dd>This attribute <em class="ct">must</em> be the number of items associated
with the object.</dd>
<dt><dfn id="cssrulelist-item" title="cssrulelist-item"><code>item(<var title="">index</var>)</code></dfn>,
method</dt>
<dd>When invoked, if <var title="">index</var> is equal or greater than the
<code title="cssrulelist-length">length</code> this method
<em class="ct">must</em> return <code>null</code>. Otherwise, this method
<em class="ct">must</em> return the <code>CSSRule</code> in the list given by
<var title="">index</var>.</dd>
<!-- XXX: Negative numbers are supposedly dealt with by the binding
language. -->
</dl>
<h3>Interfaces for CSS Statements</h3>
<p>This section defines several specific interfaces and one generic (from
which the more specific inherit) for different types of CSS statements.</p>
<h4>The <code>CSSRule</code> Interface</h4>
<pre class="idl">interface <dfn>CSSRule</dfn> {
const unsigned short <span>STYLE_RULE</span> = 1;
const unsigned short <span>CHARSET_RULE</span> = 2;
const unsigned short <span>IMPORT_RULE</span> = 3;
const unsigned short <span>MEDIA_RULE</span> = 4;
const unsigned short <span>FONT_FACE_RULE</span> = 5;
const unsigned short <span>PAGE_RULE</span> = 6;
const unsigned short <span>NAMESPACE_RULE</span> = 7;
readonly attribute unsigned short <span title="cssrule-type">type</span>;
attribute DOMString <span title="cssrule-csstext">cssText</span>;
readonly attribute <span>CSSRule</span> <span title="cssrule-parentrule">parentRule</span>;
readonly attribute <span>CSSStyleSheet</span> <span title="cssrule-parentstylesheet">parentStyleSheet</span>;
};</pre>
<p>The <dfn id="cssrule-style-rule"><code>STYLE_RULE</code></dfn>,
<dfn id="cssrule-charset-rule"><code>CHARSET_RULE</code></dfn>,