CSS Object Model (CSSOM)

Abstract

CSSOM defines APIs (including generic parsing and serialization rules) for Media Queries, Selectors, and of course CSS itself.

Status of this Document

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 or by the CSS Working Group. Don't cite this document other than as work in progress.

Implementers should note well that this specification is an ongoing effort to sort out what has been widely implemented and deployed from DOM2STYLE as well as common extensions thereto, some details of which are currently interoperable and others which are not currently interoperable. As this specification moves forward, it is hoped that these differences will be resolved and an unambiguous and adequate consensus-based specification will emerge.

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 W3C technical reports index at http://www.w3.org/TR/.

This is the [DATE: 3 August 2002] [LONGSTATUS] of CSSOM. Please send comments to www-style@w3.org (archived) with [cssom] at the start of the subject line.

This is the [DATE] First Public Working Draft of CSSOM, produced by the CSS Working Group (part of the Style Activity).

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures 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 Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Table of Contents

Introduction

This document formally specifies the core features of the CSS Object Model (CSSOM). Other documents in the CSSOM family of specifications as well as other CSS related specifications define extensions to these core features.

The core features of the CSSOM are oriented towards providing basic capabilities to author-defined scripts to permit access to and manipulation of style related state information and processes.

The features defined below are fundamentally based on prior specifications of the W3C DOM Working Group, primarily DOM2STYLE. The purposes of the present document are (1) to improve on that prior work by providing more technical specificity (so as to improve testability and interoperability), (2) to deprecate or remove certain less-widely implemented features no longer considered to be essential in this context, and (3) to newly specify certain extensions that have been or expected to be widely implemented.

A full list of the changes to API signatures can be found in Changes from DOM-2 Style.

Conformance

All diagrams, examples, and notes in this specification are non-normative, as are all sections explicitly marked non-normative. Everything else in this specification is normative.

The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this document are to be interpreted as described in RFC2119. For readability, these words do not appear in all uppercase letters in this specification. RFC2119

Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and terminate these steps") are to be interpreted with the meaning of the key word ("must", "should", "may", etc) used in introducing the algorithm.

Conformance requirements phrased as algorithms or specific steps may be implemented in any manner, so long as the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be easy to follow, and not intended to be performant.)

User agents may impose implementation-specific limits on otherwise unconstrained inputs, e.g. to prevent denial of service attacks, to guard against running out of memory, or to work around platform-specific limitations.

When a method or an attribute is said to call another method or attribute, the user agent must invoke its internal API for that attribute or method so that e.g. the author can't change the behavior by overriding attributes or methods with custom properties or functions in ECMAScript.

Unless otherwise stated, string comparisons are done in a case-sensitive manner.

Terminology

This specification employs certain terminology from the following documents: DOM4, HTML, Associating Style Sheets with XML documents and XML DOM HTML XMLSS XML.

When this specification talks about object A where A is actually an interface, it generally means an object implementing interface A.

The term whitespace is used as defined in CSS.

The terms set and clear to refer to the true and false values of binary flags or variables, respectively. These terms are also used as verbs in which case they refer to mutating some value to make it true or false, respectively.

Common Serializing Idioms

To escape a character means to create a string of "\" (U+005C), followed by the character.

To escape a character as code point means to create a string of "\" (U+005C), followed by the Unicode code point as the smallest possible number of hexadecimal digits in the range 0-9 a-f (U+0030 to U+0039 and U+0061 to U+0066) to represent the code point in base 16, followed by a single SPACE (U+0020).

To serialize an identifier means to create a string represented by the concatenation of, for each character of the identifier:

• If the character is NULL (U+0000), then throw an InvalidCharacterError exception and terminate these steps.
• If the character is in the range [\1-\1f] (U+0001 to U+001F) or [\7f-\9f] (U+007F to U+009F), then the character escaped as code point.
• If the character is the first character and is in the range [0-9] (U+0030 to U+0039), then the character escaped as code point.
• If the character is the second character and is in the range [0-9] (U+0030 to U+0039) and the first character is a "-" (U+002D), then the character escaped as code point.
• If the character is the second character and is "-" (U+002D) and the first character is "-" as well, then the escaped character.
• If the character is not handled by one of the above rules and is greater than or equal to U+0080, is "-" (U+002D) or "_" (U+005F), or is in one of the ranges [0-9] (U+0030 to U+0039), [A-Z] (U+0041 to U+005A), or [a-z] (U+0061 to U+007A), then the character itself.
• Otherwise, the escaped character.

To serialize a string means to create a string represented by '"' (U+0022), followed by the result of applying the rules below to each character of the given string, followed by '"' (U+0022):

• If the character is NULL (U+0000), then throw an InvalidCharacterError exception and terminate these steps.
• If the character is in the range [\1-\1f] (U+0001 to U+001F) or [\7f-\9f] (U+007F to U+009F), the character escaped as code point.
• If the character is '"' (U+0022) or '\' (U+005C), the escaped character.
• Otherwise, the character itself.

"'" (U+0027) is not escaped because strings are always serialized with '"' (U+0022).

To serialize a URL means to create a string represented by "url(", followed by the string escaped value of the given string, followed by ")".

To serialize a comma-separated list concatenate all items of the list in list order while separating them by ", ", i.e., COMMA (U+002C) followed by a single SPACE (U+0020).

To serialize a whitespace-separated list concatenate all items of the list in list order while separating them by " ", i.e., a single SPACE (U+0020).

When serializing a list according to the above rules, extraneous whitespace is not inserted prior to the first item or subsequent to the last item. Unless otherwise specified, an empty list is serialized as the empty string.

Media Queries

Media queries are defined by the Media Queries specification. This section defines various concepts around media queries, including their API and serialization form.

Parsing Media Queries

To parse a media query list for a given string s into a media query list is defined in the Media Queries specification. Return the list of one or more media queries that the algorithm defined there gives.

A media query that ends up being "ignored" will turn into "not all".

To parse a media query for a given string s means to follow the parse a media query list steps and return null if more than one media query is returned or a media query if a single media query is returned.

Again, a media query that ends up being "ignored" will turn into "not all".

Serializing Media Queries

To serialize a media query list run these steps:

1. If the media query list is empty return the empty string and terminate these steps.

2. Serialize each media query in the list of media queries, sort them in lexicographical order, and then serialize the list.

To serialize a media query let s be the empty string, run the steps below, and finally return s:

1. If the media query is negated append "not", followed by a single SPACE (U+0020), to s.

2. Let type be the media type of the media query, escaped and converted to ASCII lowercase.

3. If the media query does not contain media features append type, to s, then return s and terminate this algorithm.

4. If type is not "all" or if the media query is negated append type, followed by a single SPACE (U+0020), followed by "and", followed by a single SPACE (U+0020), to s.

5. Sort the media features in lexicographical order.

6. Then, for each media feature:

   1. Append a "(" (U+0028), followed by the media feature name, converted to ASCII lowercase, to s.

   2. If a value is given append a ":" (U+003A), followed by a single SPACE (U+0020), followed by the serialized media feature value, to s.

   3. Append a ")" (U+0029) to s.

   4. If this is not the last media feature append a single SPACE (U+0020), followed by "and", followed by a single SPACE (U+0020), to s.

not screen and (min-WIDTH:5px) AND (max-width:40px)

not screen and (max-width: 40px) and (min-width: 5px)

all and (color) and (color)

(color)

Serializing Media Feature Values

This should probably be done in terms of mapping it to serializing CSS values as media features are defined in terms of CSS values after all.

To serialize a media feature value named v locate v in the first column of the table below and use the serialization format described in the second column:

Other specifications can extend this table and vendor-prefixed media features can have custom serialization formats as well.

Comparing Media Queries

To compare media queries m1 and m2 means to serialize them both and return true if they are a case-sensitive match and false if they are not.

The MediaList Interface

Selectors

Selectors are defined in the Selectors specification. This section mainly defines how to serialize them.

Parsing Selectors

To parse a group of selectors means to parse the value using the selectors_group production defined in the Selectors specification and return either a group of selectors if parsing did not fail or null if parsing did fail.

Serializing Selectors

To serialize a group of selectors serialize each selector in the group of selectors and then serialize the group.

To serialize a selector let s be the empty string, run the steps below for each part of the chain of the selector, and finally return s:

1. If there is only one simple selector in the sequence of simple selectors which is a universal selector, append the result of serializing the universal selector to s.

2. Otherwise, for each simple selector in the sequence of simple selectors that is not a universal selector of which the namespace prefix maps to the null namespace (not in a namespace) or of which the namespace prefix maps to a namespace that is not the default namespace serialize the simple selector and append the result to s.

3. If this is not the last part of the chain of the selector append a single SPACE (U+0020), followed by the combinator ">", "+", or "~" as appropriate, followed by another single SPACE (U+0020) if the combinator was not whitespace, to s.

4. If this is the last part of the chain of the selector and there is a pseudo-element, append "::" followed by the name of the pseudo-class, to s.

To serialize a simple selector let s be the empty string, run the steps below, and finally return s:

type selector

universal selector

1. If the namespace prefix maps to a namespace that is not the default namespace and is not the null namespace (not in a namespace) append the escaped namespace prefix, followed by a "|" (U+007C) to s.

2. If the namespace prefix maps to a namespace that is the null namespace (not in a namespace) append "|" (U+007C) to s.

3. If this is a type selector append the escaped element name to s.

4. If this is a universal selector append "*" (U+002A) to s.

attribute selector

1. Append "[" (U+005B) to s.

2. If the namespace prefix maps to a namespace that is not the null namespace (not in a namespace) append the escaped namespace prefix, followed by a "|" (U+007C) to s.

3. If the namespace prefix maps to a namespace that is the null namespace (not in a namespace) append "|" (U+007C) to s.

4. Append the escaped attribute name to s.

5. If there is an attribute value specified, append "=", "~=", "|=", "^=", "$=", or "*=" as appropriate (depending on the type of attribute selector), followed by the string escaped attribute value, to s.

6. Append "]" (U+005D) to s.

class selector

Append a "." (U+002E), followed by the escaped class name to s.

ID selector

Append a "#" (U+0023), followed by the escaped ID to s.

pseudo-class

If the pseudo-class does not accept arguments append ":" (U+003A), followed by the name of the pseudo-class, to s.

Otherwise, append ":" (U+003A), followed by the name of the pseudo-class, followed by "(" (U+0028), followed by the value of the pseudo-class argument determined as per below, followed by ")" (U+0029), to s.

:lang()

The escaped value.

:nth-child()

:nth-last-child()

:nth-of-type()

:nth-last-of-type()

1. If the value is odd let the value be "2n+1".

2. If the value is even let the value be "2n".

3. If a is zero let the value be b serialized as <integer>.

4. If a is one or minus one and b is zero let the value be "n" (U+006E).

5. If a is one or minus one let the value be "n" (U+006E), followed by "+" (U+002B) if b is positive, followed by b serialized as <integer>.

6. If b is zero let the value be a serialized as <integer>, followed by "n" (U+006E).

7. Otherwise let the value be a serialized as <integer>, followed by "n" (U+006E), followed by "+" (U+002B) if b is positive, followed by b serialized as <integer>.

:not()

The result of serializing the value using the rules for serializing a group of selectors.

CSS

CSS Style Sheets

A CSS style sheet is an abstract concept that represents a style sheet as defined by the CSS specification. In the CSSOM a CSS style sheet is represented as a CSSStyleSheet object. A CSS style sheet has a number of associated state items:

style sheet type

The literal string "text/css".

style sheet location

The URL of the style sheet or null if the style sheet was embedded.

style sheet parent

The style sheet that is the parent of the style sheet or null if there is no associated parent.

style sheet owner node

The DOM node associated with the style sheet or null if there is no associated DOM node.

style sheet owner CSS rule

The CSS rule in the style sheet parent that caused the inclusion of the style sheet or null if there is no associated rule.

style sheet media

The MediaList object associated with the style sheet.

If this property is set to a string run the create a MediaList object steps for that string and associate the returned object with the style sheet.

style sheet title

The title of the style sheet or null if no title is specified or is the empty string, in which case the title is referred to as an empty title.

In the following, the style sheet title is non-empty for the first style sheet, but is empty for the second and third style sheets.

<style title="papaya whip">
  body { background: #ffefd5; }
</style>

<style title="">
  body { background: orange; }
</style>

<style>
  body { background: brown; }
</style>

style sheet alternate flag

Either set or clear. Clear by default.

The following style sheets have their style sheet alternate flag set:

<?xml-stylesheet alternate="yes" title="x" href="data:text/css,…"?>

<link rel="alternate stylesheet" title="x" href="data:text/css,…">

style sheet disabled flag

Either set or clear. Clear by default.

Even when clear it does not necessarily mean that the style sheet is actually used for rendering.

style sheet CSS rules

The CSS rules associated with the style sheet.

When you are to create a style sheet the above properties, with the exception of style sheet type and style sheet CSS rules, are to be set to their proper values.

The StyleSheet Interface

The CSSStyleSheet Interface

Style Sheet Collections

Below various new concepts are defined that are associated with each Document object.

Each Document has an associated list of zero or more style sheets, named the document style sheets. This is an ordered list that contains all style sheets associated with the Document, in tree order, with style sheets created from HTTP Link headers first, if any, in header order.

To create a style sheet, run these steps:

1. Create a new style sheet object and set its properties as specified.

2. Then run the add a style sheet steps for the newly created style sheet.

To add a style sheet, run these steps:

1. Add the style sheet to the list of document style sheets at the appropriate location. The remainder of these steps deal with the style sheet disabled flag.

2. If the style sheet disabled flag is set, terminate these steps.

3. If the style sheet title is non-empty, the style sheet alternate flag is clear, and preferred style sheet set name is the empty string change the preferred style sheet set name to the style sheet title.

4. If any of the following is true clear the style sheet disabled flag and terminate these steps:

   • The style sheet title is empty.

   • The last style sheet set name is null and the style sheet title is a case-sensitive match for the preferred style sheet set name.

   • The style sheet title is a case-sensitive match for the last style sheet set name.

5. Set the style sheet disabled flag.

A persistent style sheet is a style sheet from the document style sheets whose style sheet title is the empty string and whose style sheet alternate flag is clear.

A style sheet set is an ordered collection of one or more style sheets from the document style sheets which have an identical style sheet title that is not the empty string.

A style sheet set name is the style sheet title the style sheet set has in common.

An enabled style sheet set is a style sheet set of which each style sheet has its style sheet disabled flag clear.

To enable a style sheet set with name name, run these steps:

1. If name is the empty string, set the style sheet disabled flag for each style sheet that is in a style sheet set and terminate these steps.

2. Clear the style sheet disabled flag for each style sheet in a style sheet set whose style sheet set name is a case-sensitive match for name and set it for all other style sheets in a style sheet set.

To select a style sheet set with name name, run these steps:

1. Enable a style sheet set with name name.

2. Set last style sheet set name to name.

A last style sheet set name is a concept to determine what style sheet set was last selected. Initially its value is null.

A preferred style sheet set name is a concept to determine which style sheets need to have their style sheet disabled flag clear. Initially its value is the empty string.

To change the preferred style sheet set name with name name, run these steps:

1. Let current be the preferred style sheet set name.

2. Set preferred style sheet set name to name.

3. If name is not a case-sensitive match for current and last style sheet set name is null enable a style sheet set with name name.

The HTTP Default-Style Header

The HTTP Default-Style header can be used to set the preferred style sheet set name influencing which style sheet set is (initially) the enabled style sheet set.

For each HTTP Default-Style header, in header order, the user agent must change the preferred style sheet set name with name being the value of the header.

The StyleSheetList Sequence

Extensions to the Document Interface

Interaction with the User Interface

The user interface of Web browsers that support style sheets should list the style sheet titles given in the styleSheetSets list, showing the selectedStyleSheetSet as the selected style sheet set, leaving none selected if it is null or the empty string, and selecting an extra option "Basic Page Style" (or similar) if it is the empty string and the preferredStyleSheetSet is the empty string as well.

Selecting a style sheet from this list should use the select a style sheet set set of steps. This (by definition) affects the lastStyleSheetSet attribute.

Persisting the selected style sheet set

If a user agent persist the selected style sheet set, they should use the value of the selectedStyleSheetSet attribute, or if that is null, the lastStyleSheetSet attribute, when leaving the page (or at some other time) to determine the set name to store. If that is null then the style sheet set should not be persisted.

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 <head> 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 using the select a style sheet set set of steps as if the user had selected the set manually.

This specification does not give any suggestions on how user agents should decide to persist the style sheet set or whether or how to persist the selected set across pages.

Examples

<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">

<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>

Style Sheet Association

This section defines the interface a style sheet owner node of a style sheet has to implement and defines the requirements for xml-stylesheet processing instructions and HTTP Link headers when the link relation type is an ASCII case-insensitive match for "stylesheet" since nobody else was interested in defining this.

The editor is in good hope that HTML and SVG will define the appropriate processing in their respective specifications, in terms of this specification, in due course.

The LinkStyle Interface

<style type="text/css">
  body { background:lime }
</style>

<style type="text/example-sheets">
  $(body).background := lime
</style>

Whether or not the node refers to a style sheet is defined by the specification that defines the semantics of said node.

Requirements on specifications

Specifications introducing new ways of associating style sheets through the DOM should define which nodes implement the LinkStyle interface. When doing so, they must also define when a style sheet is created.

Requirements on User Agents Implementing the xml-stylesheet processing instruction

For each xml-stylesheet processing instruction that is not part of the document type declaration and has an href pseudo-attribute these steps must (unless otherwise stated) be run:

1. Let title be the value of the title pseudo-attribute or the empty string if the title pseudo-attribute is not specified.

2. If there is an alternate pseudo-attribute whose value is a case-sensitive match for "yes" and title is the empty string terminate these steps.

3. If there is a type pseudo-attribute whose value is not a supported styling language the user agent may terminate these steps.

4. Resolve the URL specified by the href pseudo-attribute and then fetch it.

5. When the resource is available, the document is in quirks mode and the Content-Type metadata of the resource is not a supported styling language change the Content-Type metadata of the resource to text/css.

   This step might never actually happen, but is included here in case other specifications change, to keep things consistent.

6. If the resource is not in a supported styling language terminate these steps.

7. Create a style sheet with the following properties:

   style sheet location

   The absolute URL of the resource.

   style sheet parent

   null

   style sheet owner node

   The node.

   style sheet owner CSS rule

   null

   style sheet media

   The value of the media pseudo-attribute if any, or the empty string otherwise.

   style sheet title

   title

   style sheet alternate flag

   Set if the alternate pseudo-attribute value is a case-sensitive match for "yes", or clear otherwise.

Requirements on User Agents Implementing the HTTP Link Header

For each HTTP Link header of which one of the link relation types is an ASCII case-insensitive match for "stylesheet" these steps must be run:

1. Let title be the value of the first of all the title and title* parameters. If there are no such parameters it is the empty string.

2. If one of the (other) link relation types is an ASCII case-insensitive match for "alternate" and title is the empty string terminate these steps.

3. Resolve the specified URL and fetch it.

4. When the resource is available, the document is in quirks mode and the Content-Type metadata of the resource is not a supported styling language change the Content-Type metadata of the resource to text/css.

5. If the resource is not in a supported styling language terminate these steps.

6. Create a style sheet with the following properties:

   style sheet location

   The absolute URL of the resource.

   style sheet owner node

   null

   style sheet parent

   null

   style sheet owner CSS rule

   null

   style sheet media

   The value of the first media parameter.

   style sheet title

   title

   style sheet alternate flag

   Set if one of the specified link relation type for this HTTP Link header is an ASCII case-insensitive match for "alternate", or false otherwise.

CSS Rules

A CSS rule is an abstract concept that denotes a rule as defined by the CSS specification. A CSS rule is represented as an object that implements a subclass of the CSSRule interface, and which has the following associated state items:

rule type

A non-negative integer associated with a particular type of rule. This item is initialized when a rule is created and must never change.

rule text

A text representation of the rule suitable for direct use in a style sheet. This item is initialized when a rule is created, and may change over the lifetime of the rule.

rule parent

An optional reference to another, enclosing CSS rule. If the rule has an enclosing rule when it is created, then this item is initialized to the enclosing rule; otherwise it is null. Subsequent to initialization, this item is reset to null if the rule becomes non-enclosed. Once reset to null, it must never change.

rule parent style sheet

An optional reference to an associated CSS style sheet. This item is initialized to reference an associated style sheet when the rule is created. Subsequent to initialization, this item is reset to null if the rule becomes disassociated from its initial style sheet. Once reset to null, it must never change.

In addition to the above state, each CSS rule may be associated with other state in accordance with its rule type.

To parse a CSS rule ...

Should a rule be instantiated in OM if there is a parse error? To what extent should original (but non-valid) CSS text be captured in cssText?

To serialize a CSS rule, perform one of the following in accordance with the rule's type:

CSSStyleRule

The result of concatenating the following:

1. The result of performing serialize a group of selectors on the rule's associated selectors.
2. The string " { ", i.e., a single SPACE (U+0020), followed by LEFT CURLY BRACKET (U+007B), followed by a single SPACE (U+0020).
3. The result of performing serialize a CSS declaration block on the rule's associated declarations.
4. If the rule is associated with one or more declarations, the string " ", i.e., a single SPACE (U+0020).
5. The string "}", RIGHT CURLY BRACKET (U+007D).

CSSCharsetRule

The result of concatenating the following:

1. The string "@charset" followed by a single SPACE (U+0020).
2. The result of performing serialize a string on the preferred MIME name of the rule's encoding.
3. The string ";", i.e., SEMICOLON (U+003B).

@charset "UTF-8";

CSSImportRule

The result of concatenating the following:

1. The string "@import" followed by a single SPACE (U+0020).
2. The result of performing serialize a URL on the rule's location.
3. If the rule's associated media list is not empty, a single SPACE (U+0020) followed by the result of performing serialize a media query list on the media list.
4. The string ";", i.e., SEMICOLON (U+003B).

@import url("import.css");

@import url("print.css") print;

CSSMediaRule

...

CSSFontFaceRule

...

CSSPageRule

...

CSSNamespaceRule

The literal string "@namespace", followed by a single SPACE (U+0020), followed by the identifier escaped value of the prefix attribute (if any), followed by a single SPACE (U+0020) if there is a prefix, followed by the URL escaped value of the namespaceURI attribute, followed the character ";" (U+003B).

The CSSRuleList Sequence

The CSSRule Interface

The CSSStyleRule Interface

The CSSCharsetRule Interface

The CSSImportRule Interface

The CSSMediaRule Interface

The CSSFontFaceRule Interface

The CSSPageRule Interface

The CSSNamespaceRule Interface

CSS Declaration Blocks

A CSS declaration block is an ordered collection of CSS properties with their associated values, also named CSS declarations. In the DOM a CSS declaration block is a CSSStyleDeclaration object. A CSS declaration block has two associated properties:

CSS declaration block readonly flag

Clear if the object can be manipulated. Set if it can not be manipulated. Unless otherwise stated it is clear.

CSS declaration block declarations

The CSS declarations associated with the object.

The CSS declaration block declarations are ordered. This matters for the item() method.

To parse a CSS declaration block ...

What should be captured in the cssText of a declaration block which fails to parse?

To serialize a CSS declaration block represented by a CSSStyleDeclarations instance named d, let s be the empty string, then run the steps below:

1. If d.length is zero (0), then return s.

2. For each i from zero (0) through d.length - 1 (inclusive), perform the following sub-steps:

   1. Let n be the value returned by d.item(i).

   2. Let v be the value returned by d.getPropertyValue(n).

   3. If v is the empty string, then continue.

   4. Otherwise (v is non-empty), perform the following sub-steps:

      1. If s is not empty, then append a single SPACE (U+0020) to s.

      2. Append n to s.

      3. Append COLON (U+003A) followed by a single SPACE (U+0020), i.e., ": ", to s.

      4. Append v to s.

   5. Let p be the value returned by d.getPropertyPriority(n).

   6. If p is not the empty string, then perform the following sub-steps:

      1. Append a single SPACE (U+0020) followed by EXCLAMATION MARK (U+0021), i.e., " !", to s.

      2. Append p to s.

   7. Append SEMICOLON (U+003B), i.e., ";", to s.

3. Return s.

The serialization of an empty CSS declaration block is the empty string.

The serialization of a non-empty CSS declaration block does not include any surrounding whitespace, i.e., no whitepsace appears before the first property name and no whitespace appears after the final semicolon delimiter that follows the last property value.

The CSSStyleDeclaration Interface

For the table below, the IDL attribute in the first column must return the result of invoking getPropertyValue() with as argument the CSS property given in the second column on the same row.

Similarly for the table below, setting the IDL attribute in the first column must invoke setProperty() with as first argument the CSS property given in the second column on the same row, as second argument the given value, and no third argument. Any exceptions thrown must be re-thrown.

Restore the entries for the following table or resurrect CSS2Properties (or similar) or define in general terms using prose or ...

CSS Values

Parsing CSS Values

To parse a CSS value for a given property means to a parse the given value according to the definition of the property that is an ASCII case-insensitive match for property in the CSS specification. If the given value is ignored return null. Otherwise return the CSS value for the given property.

"!important" declarations are not part of the property value space and will therefore cause parse a CSS value to return null.

Serializing CSS Values

To serialize a CSS value follow these rules:

• Serialize any CSS component values in the value.

• Where multiple CSS component values can appear in any order without changing the meaning of the value (typically represented by a double bar || in the value syntax), use the order as given in the syntax.

• Where CSS component values of the value can be omitted without changing the meaning of the value (e.g. initial values in shorthand properties), omit them. If this would remove all the values, then include the first allowed value.

  E.g. margin: 20px 20px becomes margin: 20px.

  E.g. the value 0 for the 'border' property.

• If the value of a shorthand property is requested and it cannot be computed because the properties associated with the shorthand have values that cannot be represented by the shorthand the serialization is the empty string.

• If a value has a whitespace-separated list of CSS component values, serialize the value as a whitespace-separated list.

• If a value has a comma-separated list of CSS component values, serialize the value as a comma-separated list.

To serialize a CSS component value depends on the component, as follows:

keyword

The keyword converted to ASCII lowercase.

<angle>

The number of degrees serialized as per <number> followed by the literal string "deg".

<color>

If <color> is a component of a resolved or computed value, then return the color using the rgb() or rgba() functional notation as follows:

1. If the alpha component of the color is equal to one, then return the serialization of the rgb() functional equivalent of the opaque color.
2. If the alpha component of the color is not equal to one, then return the serialization of the rgba() functional equivalent of the non-opaque color.

The serialization of the rgb() functional equivalent is the concatenation of the following:

1. The string "rgb(".
2. The shortest base-ten integer serialization of the color's red component.
3. The string ", ".
4. The shortest base-ten serialization of the color's green component.
5. The string ", ".
6. The shortest base-ten serialization of the color's blue component.
7. The string ")".

The serialization of the rgba() functional equivalent is the concatenation of the following:

1. The string "rgba(".
2. The shortest base-ten serialization of the color's red component.
3. The string ", ".
4. The shortest base-ten serialization of the color's green component.
5. The string ", ".
6. The shortest base-ten serialization of the color's blue component.
7. The string ", ".
8. The shortest serialization of the <number> that denotes the color's alpha component.
9. The string ")".

In the above rules, the string ", " denotes a COMMA (U+002C) followed by a single SPACE (U+0020).

If <color> is a component of a specified value, then return the color as follows:

1. If the color was explicitly specified by the author, then return the original, author specified color value.
2. Otherwise, return the value that would be returned if the color were a component of a computed value.

Should author specified values be normalized for case? Or should original case be preserved?

<counter>

The concatenation of:

1. If <counter> has three CSS component values the string "counters(".

2. If <counter> has two CSS component values the string "counter(".

3. The result of serializing the serialized CSS component values belonging to <counter> as list while omitting the last CSS component value if it is 'decimal'.

4. ")" (U+0029).

<frequency>

The frequency in hertz serialized as per <number> followed by the literal string "hz".

<identifier>

The identifier escaped.

<integer>

A base-ten integer using digits 0-9 (U+0030 to U+0039) in the shortest form possible, preceded by "-" (U+002D) if it is negative.

<length>

A length of zero is represented by the literal string "0px".

Absolute lengths: the number of millimeters serialized as per <number> followed by the literal string "mm".

Rumor has it absolute lengths will become relative lengths. Centimeters would be compatible with <resolution>...

Relative lengths: the <number> component serialized as per <number> followed by the unit in its canonical form as defined in its respective specification.

<number>

Browsers seem to use ToString(), but that might give a significand which according to some is teh evil (and also currently does not parse correctly).

<percentage>

The <number> component serialized as per <number> followed by the literal string "%" (U+0025).

<resolution>

The resolution in dots per centimeter serialized as per <number> followed by the literal string "dpcm".

<shape>

The string "rect(", followed by the result of serializing the serialized CSS component values belonging to <shape> as list, followed by ")" (U+0029).

<string>

<family-name>

<specific-voice>

The string string escaped.

<time>

The time in seconds serialized as per <number> followed by the literal string "s".

<uri>

The absolute URL URL escaped.

<absolute-size>, <border-width>, <border-style>, <bottom>, <generic-family>, <generic-voice>, <left>, <margin-width>, <padding-width>, <relative-size>, <right>, and <top>, are considered macros by this specification. They all represent instances of components outlined above.

One idea is that we can remove this section somewhere in the CSS3/CSS4 timeline by moving the above definitions to the drafts that define the CSS components.

Examples

Here are some examples of before and after results on specified values. The before column could be what the author wrote in a style sheet, while the after column shows what querying the DOM would return.

DOM Access to CSS Declaration Blocks

The ElementCSSInlineStyle Interface

Extensions to the Window Interface

Resolved Values

getComputedStyle() was historically defined to return the "computed value" of an element or pseudo-element. However, the concept of "computed value" changed between revisions of CSS while the implementation of getComputedStyle() had to remain the same for compatibility with deployed scripts. To address this issue this specification introduces the concept of a resolved value.

The resolved value for a given property can be determined as follows:

'line-height'

The resolved value is the used value.

'height'

'margin'

'margin-bottom'

'margin-left'

'margin-right'

'margin-top'

'padding'

'padding-bottom'

'padding-left'

'padding-right'

'padding-top'

'width'

If the property applies to the element or pseudo-element and the resolved value of the 'display' property is not none, the resolved value is the used value. Otherwise the resolved value is the computed value.

'bottom'

'left'

'right'

'top'

If the property applies to a positioned element and the resolved value of the 'display' property is not none, the resolved value is the used value. Otherwise the resolved value is the computed value.

Any other property

The resolved value is the computed value.

IANA Considerations

Default-Style

This section describes a header field for registration in the Permanent Message Header Field Registry.

Header field name

Default-Style

Applicable protocol

http

Status

standard

Author/Change controller

W3C

Specification document(s)

This document is the relevant specification.

Related information

None.

References

Normative references

Informative references

Change History

This section documents the primary technical changes of CSSOM related functionality, with a focus on changes to API signatures.

Changes From DOM-2 Style

• Remove definition of CSSRule.UNKNOWN_RULE, reserving its value (0) to prevent future reuse.

• Remove definition of DOMImplementationCSS interface.

Acknowledgments

The editors would like to thank Alexey Feldgendler, Björn Höhrmann, Boris Zbasky, Brian Kardell, Christian Krebs, Daniel Glazman, David Baron, fantasai, Hallvord R. M. Steen, Ian Hickson, John Daggett, Lachlan Hunt, Morten Stenshorne, Philip Taylor, Robert O'Callahan, Sjoerd Visscher, Simon Pieters, Sylvain Galineau, Tarquin Wilton-Jones, and Zack Weinberg for contributing to this specification.

Additional thanks to Ian Hickson for writing the initial version of the alternative style sheets API and canonicalization (now serialization) rules for CSS values.