CSS Pseudo-Elements Module Level 4

Editor’s Draft,

Specification Metadata
This version:
https://drafts.csswg.org/css-pseudo-4/
Latest published version:
https://www.w3.org/TR/css-pseudo-4/
Previous Versions:
Test Suite:
http://test.csswg.org/suites/css-pseudo-4_dev/nightly-unstable/
Issue Tracking:
CSSWG Issues Repository
Inline In Spec
Editors:
Daniel Glazman (Disruptive Innovations)
Elika J. Etemad / fantasai (Invited Expert)
(Adobe Systems Inc.)
Suggest an Edit for this Spec:
GitHub Editor
Issues List:
Tracked in Editor’s Draft

Abstract

This CSS module defines pseudo-elements, abstract elements that represent portions of the CSS render tree that can be selected and styled.

CSS is a language for describing the rendering of structured documents (such as HTML and XML) on screen, on paper, etc.

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. Don’t cite this document other than as work in progress.

Please send feedback by filing issues in GitHub (preferred), including the spec code “css-pseudo” in the title, like this: “[css-pseudo] …summary of comment…”. All issues and comments are archived. Alternately, feedback can be sent to the (archived) public mailing list www-style@w3.org.

This document is governed by the 15 September 2020 W3C Process Document.

1. Introduction

This section is informative.

Pseudo-elements represent abstract elements of the document beyond those elements explicitly created by the document language. Since they are not restricted to fitting into the document tree, they can be used to select and style portions of the document that do not necessarily map to the document’s tree structure. For instance, the ::first-line pseudo-element can select content on the first formatted line of an element after text wrapping, allowing just that line to be styled differently from the rest of the paragraph.

Each pseudo-element is associated with an originating element and has syntax of the form ::name-of-pseudo. This module defines the pseudo-elements that exist in CSS and how they can be styled. For more information on pseudo-elements in general, and on their syntax and interaction with other selectors, see [SELECTORS-4].

2. Typographic Pseudo-elements

2.1. The ::first-line pseudo-element

::first-line

In all current engines.

Firefox1+Safari1+Chrome1+
Opera7+Edge79+
Edge (Legacy)12+IE9+
Firefox for Android4+iOS Safari1+Chrome for Android18+Android WebView37+Samsung Internet1.0+Opera Mobile10.1+

The ::first-line pseudo-element represents the contents of the first formatted line of its originating element.

The rule below means “change the letters of the first line of every p element to uppercase”:
p::first-line { text-transform: uppercase }

The selector p::first-line does not match any real document element. It instead matches a pseudo-element that the user agent will automatically insert at the beginning of every p element.

Note: Note that the length of the first line depends on a number of factors, including the width of the page, the font size, etc.

For example, given an ordinary HTML [HTML5] paragraph such as:
<P>This is a somewhat long HTML paragraph
that will be broken into several lines.
The first line will be styled
by the ‘::first-line’ pseudo-element.
The other lines will be treated
as ordinary lines in the paragraph.</P>

Depending on the width of the element, its lines might be broken as follows:

THIS IS A SOMEWHAT LONG HTML PARAGRAPH THAT
will be broken into several lines. The
first line will be by the ‘::first-line’
pseudo-element. The other lines will be
treated as ordinary lines in the paragraph.

or alternately as follows:

THIS IS A SOMEWHAT LONG
HTML paragraph that will
be broken into several
lines. The first line will
be by the ‘::first-line’
pseudo-element. The other
lines will be treated as
ordinary lines in the
paragraph.

2.1.1. Finding the First Formatted Line

In CSS, the ::first-line pseudo-element can only have an effect when attached to a block container:

Note: The first formatted line can be an empty line. For example, the first line of the p in <p><br>First… doesn’t contain any letters. Thus the word “First” is not on the first formatted line, and will not be affected by p::first-line.

Note: The first line of a block container that does not participate in a block formatting context cannot be the first formatted line of an ancestor element. Thus, in <DIV><P STYLE="display: inline-block">Hello<BR>Goodbye</P> etcetera</DIV> the first formatted line of the DIV is not the line “Hello”, but rather the (otherwise empty) line that contains that entire inline block.

When a first formatted line is represented by multiple ::first-line pseudo-elements, they are nested in the same order as their originating elements.

Consider the following markup:
<DIV>
  <P>First paragraph</P>
  <P>Second paragraph</P>
</DIV>

If we assume a fictional tag sequence to represent the elements’ ::first-line pseudo elements, it would be something like:

<DIV>
  <P><DIV::first-line><P::first-line>First paragraph</P::first-line></DIV::first-line></P>
  <P><P::first-line>Second paragraph</P::first-line></P>
</DIV>

2.1.2. Styling the First Line Pseudo-element

The ::first-line pseudo-element’s generated box behaves similar to that of an inline-level element, but with certain restrictions. The following CSS properties apply to a ::first-line pseudo-element:

User agents may apply other properties as well except for the following excluded properties:

2.1.3. Inheritance and the ::first-line Pseudo-element

During CSS inheritance, the fragment of a child that occurs on the first line inherits any standard inherited propertiesexcept the properties excluded above—from the ::first-line pseudo-element. For all other properties, including all custom properties [CSS-VARIABLES-1], inheritance is from the non-pseudo parent. (The portion of a child element that does not occur on the first line always inherits from the non-pseudo parent.)

In the common case (of standard inherited CSS properties), inheritance into and from a ::first-line pseudo-element can be understood by writing out a fictional tag sequence to represent ::first-line. Consider the earlier example; in case of the first rendering, the fictional tag sequence would be:
<P><p::first-line>This is a somewhat long HTML paragraph
that</p::first-line> will be broken into several lines.
The first line will be styled
by the ‘::first-line’ pseudo-element.
The other lines will be treated
as ordinary lines in the paragraph.</p>

And in the case of the second rendering:

<p><p::first-line>This is a somewhat long</p::first-line> HTML paragraph
that will be broken into several lines.
The first line will be styled
by the ‘::first-line’ pseudo-element.
The other lines will be treated
as ordinary lines in the paragraph.</p>
If a pseudo-element breaks up a real element, the effect can often be described by a fictional tag sequence that closes and then re-opens the element. Suppose we mark up the earlier example with a span element encompassing the first sentence:
<p><span>This is a somewhat long HTML paragraph
that will be broken into several lines.</span>
The first line will be styled
by the ‘::first-line’ pseudo-element.
The other lines will be treated
as ordinary lines in the paragraph.</p>

The effect of the first rendering would be similar to the following fictional tag sequence:

<p><p::first-line><span>This is a somewhat long HTML paragraph
that</span></p::first-line><span> will be broken into several lines.</span>
The first line will be styled
by the ‘::first-line’ pseudo-element.
The other lines will be treated
as ordinary lines in the paragraph.</p>

2.2. The ::first-letter pseudo-element

::first-letter

In all current engines.

Firefox1+Safari1+Chrome1+
Opera7+Edge79+
Edge (Legacy)12+IE9+
Firefox for Android4+iOS Safari1+Chrome for Android18+Android WebView37+Samsung Internet1.0+Opera Mobile10.1+

The ::first-letter pseudo-element represents the first typographic letter unit [CSS-TEXT-3] on the first formatted line of its originating element, its first-letter text. The ::first-letter pseudo-element can be used to create “initial caps” and “drop caps”, which are common typographic effects.

For example, the following rule creates a 2-line drop-letter on every paragraph following a level-2 header, using the initial-letter property defined in [CSS-INLINE-3]:
h2 + p::first-letter { initial-letter: 2; }

As explained in [CSS-TEXT-3], a typographic letter unit can include more than one Unicode codepoint. For example, combining characters must be kept with their base character. Also, languages may have additional rules about how to treat certain letter combinations. In Dutch, for example, if the letter combination "ij" appears at the beginning of an element, both letters should be considered within the ::first-letter pseudo-element. [UAX29] When selecting the first-letter text, the UA should tailor its definition of typographic letter unit to reflect the first-letter traditions of the ::first-letter pseudo-element’s containing block’s content language.

Note: Note that the first typographic letter unit may in fact be a digit, e.g., the “6” in “67 million dollars is a lot of money.”

Punctuation (i.e, characters that belong to the Punctuation (P*) Unicode general category [UAX44]) that precedes or follows the first typographic letter unit and any intervening space separators (characters that belong to the Zs Unicode general category [UAX44]) must also be included as part of the first-letter text in the ::first-letter pseudo-element.

Quotes that precede the first letter should be included.

2.2.1. Finding the First Letter Text

As with ::first-line, the ::first-letter pseudo-element can only have an effect when attached to a block container. Its first-letter text is the first such inline-level content participating in the inline formatting context of its originating element’s first formatted line, if it is not preceded by any other in-flow content (such as images or inline tables) on its line.

For this purpose, any marker boxes are ignored, as if they were out-of-flow. However, if an element has in-flow ::before or ::after content, the first-letter text is selected from the content of the element including that generated content.

Example: After the rule p::before {content: "Note: "}, the selector p::first-letter matches the "N" of "Note".

If no such text exists, then there is no first-letter text and no ::first-letter pseudo-element.

Note: When the first formatted line is empty, ::first-letter will not match anything. For example, in this HTML fragment: <p><br>First... the first line doesn’t contain any letters, so ::first-letter doesn’t match anything. In particular, it does not match the “F” of “First”, which is on the second line.

Note: As with ::first-line, the first-letter text of a block container that does not participate in a block formatting context cannot be the first-letter text of an ancestor element. Thus, in <DIV><P STYLE="display: inline-block">Hello<BR>Goodbye</P> etcetera</DIV> the first letter of the DIV is not the letter “H”. In fact, the DIV doesn’t have a first letter, as its first formatted line contains no content besides the inline block.

2.2.2. Inheritance and Box Tree Structure of the ::first-letter Pseudo-element

The ::first-letter pseudo-element is wrapped immediately around the first-letter text it represents, even if that text is in a descendant. When a first-letter text is represented by multiple ::first-letter pseudo-elements, they are nested in the same order as their originating elements. Inheritance behaves accordingly.

Consider the following markup:
<div>
  <p><span>The first few words</span>
  and the rest of the paragraph.
</div>

If we assume a fictional tag sequence to represent the elements’ ::first-letter pseudo-elements, it would be something like:

<div>
  <p><span><div::first-letter><p::first-letter>T</…></…>he first few words</span>
  and the rest of the paragraph.
</div>

If the characters that would form the first-letter text are not all in the same element (as the ‘T in <p>‘<em>T...), the user agent may create a ::first-letter pseudo-element from one of the elements, or all elements, or simply not create a pseudo-element. Additionally, if the first-letter text is not at the start of the line (for example due to bidirectional reordering, or due to a list item marker with list-style-position: inside), then the user agent is not required to create the pseudo-element(s).

A ::first-letter pseudo-element is contained within any ::first-line pseudo-elements, and thus inherits (potentially indirectly) from ::first-line, the same as any inline box on the same line.

2.2.3. Styling the ::first-letter Pseudo-element

In CSS a ::first-letter pseudo-element is similar to an inline box. The following properties that apply to ::first-letter pseudo-elements:

User agents may apply other properties as well. However, in no case may the application of such unlisted properties to ::first-letter change what first-letter text is represented by that ::first-letter.

Note: In previous levels of CSS, user agents were allowed to choose a line height, width, and height based on the shape of the letter, to approximate font sizes; and to take the glyph outline into account when performing layout. The possibility of such loosely-defined magic has been intentionally removed, as it proved to be a poor solution for the intended use case (drop caps and raised caps), yet caused interoperability problems. See initial-letter in [CSS-INLINE-3] for explicitly handling drop caps and raised caps.

3. Highlight Pseudo-elements

3.1. Selecting Highlighted Content: the ::selection, ::target-text, ::spelling-error, and ::grammar-error pseudo-elements

The highlight pseudo-elements represent portions of a document that have been given a particular status and are typically styled differently to indicate that status to the user. For example, selected portions of the document are typically highlighted (given alternate background and foreground colors, or a color wash) to indicate their selected status. The following highlight pseudo-elements are defined:

::selection

In all current engines.

Firefox62+Safari1.1+Chrome1+
Opera9.5+Edge79+
Edge (Legacy)12+IE9+
Firefox for Android62+iOS Safari1+Chrome for Android18+Android WebView37+Samsung Internet1.0+Opera Mobile14+
::selection
Tests
The ::selection pseudo-element represents the portion of a document that has been selected as the target or object of some possible future user-agent operation(s). It applies, for example, to selected text within an editable text field, which would be copied by a copy operation or replaced by a paste operation.

::target-text

In only one current engine.

FirefoxNoneSafariNoneChrome89+
Opera75+Edge89+
Edge (Legacy)NoneIENone
Firefox for AndroidNoneiOS SafariNoneChrome for Android89+Android WebView89+Samsung InternetNoneOpera MobileNone
::target-text
The ::target-text pseudo-element represents text directly targeted by the document URL’s fragment, if any.

Note: When a URL fragment targets an element, the :target pseudo-element can be used to select it, but ::target-text does not match anything. It only matches text that is itself targeted by the [fragment].

::spelling-error

In no current engines.

FirefoxNoneSafariNoneChromeNone
OperaNoneEdgeNone
Edge (Legacy)NoneIENone
Firefox for AndroidNoneiOS SafariNoneChrome for AndroidNoneAndroid WebViewNoneSamsung InternetNoneOpera MobileNone
::spelling-error
The ::spelling-error pseudo-element represents a portion of text that has been flagged by the user agent as misspelled.
Tests

::grammar-error

In no current engines.

FirefoxNoneSafariNoneChromeNone
OperaNoneEdgeNone
Edge (Legacy)NoneIENone
Firefox for AndroidNoneiOS SafariNoneChrome for AndroidNoneAndroid WebViewNoneSamsung InternetNoneOpera MobileNone
::grammar-error
The ::grammar-error pseudo-element represents a portion of text that has been flagged by the user agent as grammatically incorrect.
Tests

The highlight pseudo-elements do not necessarily fit into the element tree, and can arbitrarily cross element boundaries without honoring its nesting structure.

Note: A future level of CSS may introduce ways to create custom highlight pseudo-elements.

3.2. Styling Highlights

The highlight pseudo-elements can only be styled by a limited set of properties that do not affect layout and can be applied performantly in a highly dynamic environment—and additionally (to ensure interoperability) whose rendering within the required area is not dependent on the exact (UA-determined) bounds of the highlight overlay. The following properties apply to the highlight pseudo-elements:

Are there any other properties that should be included here?

The color property specifies the color of both the text and all line decorations (underline, overline, line-through) and emphasis marks (text-emphasis) applied to the text by the originating element and its ancestors and descendants.

Note: Historically (and at the time of writing) only color and background-color have been interoperably supported.

3.3. Default UA Styles

The following additions are recommended for the default UA stylesheet:

/* Represent default spelling/grammar error styling in an adjustable way */
:root::spelling-error { text-decoration-line: spelling-error; }
:root::grammar-error  { text-decoration-line: grammar-error; }
/* Highlight targeted text */
:root::target-text    { color: MarkText; background: Mark; }

UAs may apply additional effects to enhance the presentation of highlighted content, for example dimming content other than the highlighted text or transitioning out a highlight style based on user interactions or timing. These are not controlled by CSS.

3.4. Area of a Highlight

For each type of highlighting (see § 3.1 Selecting Highlighted Content: the ::selection, ::target-text, ::spelling-error, and ::grammar-error pseudo-elements) there exists a single highlight overlay for the entire document, the active portions of which are represented by the corresponding highlight pseudo-element. Each box owns the piece of the overlay corresponding to any text or replaced content directly contained by the box.

See F2F minutes, dbaron’s message, Daniel’s thread, Gecko notes, Opera notes, Webkit notes

Not sure if this is the correct way of describing the way things work.

3.5. Cascading and Per-Element Highlight Styles

Each element draws its own active portions of the highlight overlays, which receives the styles specified by the corresponding highlight pseudo-element styles for which that element is the originating element. When multiple styles conflict, the winning style is determined by the cascade. When any supported property is not given a value by the cascade, it’s value is determined by inheritance from the corresponding highlight pseudo-element of its originating element’s parent element (regardless of whether that property is an inherited property).

Tests
For example, if the following rules were applied:
p::selection      { color: yellow; background: green; }
p > em::selection { color: orange; }
em::selection     { color:    red; }

to the following markup:

<p>Highlight this <em>and this</em>.</p>

The selection highlight would be green throughout, with yellow text outside the <em> element and orange text inside it.

Tests

Authors wanting multiple selections styles should use :root::selection for their document-wide selection style, since this will allow clean overriding in descendants. ::selection alone applies to every element in the tree, overriding the more specific styles of any ancestors.

For example, if an author specified
::selection          { background: blue; }
p.warning::selection { background:  red; }

and the document included

<p class="warning">Some <strong>very important information</strong></p>

The highlight would be blue over “very important information” because the <strong> element´s ::selection also matches the ::selection { background: blue; } rule. (Remember that * is implied when a tag selector is missing.) The style rules that would give the intended behavior (red highlight within p.warning, blue elsewhere) are

:root::selection     { background: blue; }
p.warning::selection { background:  red; }
Tests

The UA must use its own highlight colors for ::selection only when neither color nor background-color has been specified by the author.

Note: This paired-cascading behavior does not allow using the normal cascade (i.g. :root::selection rules in the UA style sheet) to represent the OS default selection colors. However it has been interoperably implemented in browsers and is thus probably a Web-compatibility requirement.

3.6. Painting the Highlight

Tests

3.6.1. Backgrounds

Each highlight pseudo-element draws its background over the corresponding portion of the highlight overlay, painting it immediately below any positioned descendants (i.e. just before step 8 in CSS2.2§E.2). The ::selection overlay is drawn over the ::target-text overlay which is drawn over the ::spelling-error overlay which is drawn over the ::grammar-error overlay.

Tests

3.6.2. Shadows

Any text-shadow applying to a highlight pseudo-element is drawn over its corresponding highlight overlay background. Such text shadows also stack over each other (and over any original text-shadow applied to the text and its decorations, which continues to apply).

Note: Since each highlight overlay background is drawn over any shadows belonging to the layer(s) below, a highlight overlay background can obscure lower-level shadows.

3.6.3. Text and Text Decorations

A highlight pseudo-element suppresses the normal drawing of any associated text (and the text decorations that had been applied to that text). Instead the topmost active highlight overlay redraws that text (and those decorations) over the highlight overlay backgrounds using the highlight’s own color.

For this purpose, currentColor on a highlight pseudo-element’s color property represents the color of the next highlight pseudo-element layer below, falling back finally to the colors that would otherwise have been used (those applied by the originating element or an intervening pseudo-element such as ::first-line or ::first-letter).

Any text decorations introduced by each highlight pseudo-element are stacked in the same order as their backgrounds over the text’s original decorations and are all drawn, each decoration in its own color.

Note: The element’s own text decorations (both line decorations and emphasis marks) are thus drawn in the pseudo-element’s own color when that is not currentColor, regardless of their original color or fill specifications.

3.6.4. Replaced Elements

For non-replaced content, the UA must honor the color and background-color (including their alpha channels) as specified. However, for replaced content, the UA should create a semi-transparent wash to coat the content so that it can show through the selection. This wash should be of the specified background-color if that is not transparent, else of the specified color; however the UA may adjust the alpha channel.

Tests

3.7. Security and Privacy Considerations

Because the styling of spelling and grammar errors can leak information about the contents of a user’s dictionary (which can include the user’s name and even includes the contents of his/her address book!) UAs that implement ::spelling-error and ::grammar-error must prevent pages from being able to read the styling of such highlighted segments.

4. Tree-Abiding Pseudo-elements

Tree-abiding pseudo-elements always fit within the box tree. They inherit any inheritable properties from their originating element; non-inheritable properties take their initial values as usual. [CSS-CASCADE-4]

4.1. Generated Content Pseudo-elements: ::before and ::after

::after

In all current engines.

Firefox1.5+Safari4+Chrome1+
Opera7+Edge79+
Edge (Legacy)12+IE9+
Firefox for Android4+iOS Safari3.2+Chrome for Android18+Android WebView37+Samsung Internet1.0+Opera Mobile10.1+

::before

In all current engines.

Firefox1.5+Safari4+Chrome1+
Opera7+Edge79+
Edge (Legacy)12+IE9+
Firefox for Android4+iOS Safari5.1+Chrome for Android18+Android WebView37+Samsung Internet1.0+Opera Mobile10.1+

When their computed content value is not none, these pseudo-elements generate boxes as if they were immediate children of their originating element, with content as specified by content.

::before
Represents a styleable child pseudo-element immediately before the originating element’s actual content.
::after
Represents a styleable child pseudo-element immediately after the originating element’s actual content.

These pseudo-elements can be styled exactly like any normal document-sourced element in the document tree; all properties that apply to a normal element likewise apply to ::before and ::after.

For example, the following rule inserts the string “Note: ” before the content of every <p> element whose class attribute has the value note:
p.note::before { content: "Note: " }

Since the initial value of display is inline, this will generate an inline box. Like other inline children of <p>, it will participate in <p>’s inline formatting context, potentially sharing a line with other content.

As with the content of regular elements, the generated content of ::before and :after pseudo-elements can form part of any ::first-line and ::first-letter pseudo-elements applied to its originating element.

4.2. List Markers: the ::marker pseudo-element

::marker

Firefox68+SafariNoneChrome86+
Opera72+Edge86+
Edge (Legacy)NoneIENone
Firefox for Android68+iOS SafariNoneChrome for Android86+Android WebView86+Samsung InternetNoneOpera Mobile61+

The ::marker pseudo-element represents the automatically generated marker box of a list item. (See [CSS-DISPLAY-3] and [CSS-LISTS-3].)

The contents of a ::marker are ignored (not selected) by ::first-letter.

Interaction of ::marker and ::first-line is currently under discussion in Issue 4506.

Only a limited set of properties can be used on the ::marker pseudo-element. This list is defined in CSS Lists 3 §3.1.1 Properties Applying to ::marker.

The ::before::marker or ::after::marker selectors are valid and can be used to represent the marker boxes of ::before or ::after pseudo-elements that happen to be list items. However ::marker::marker is invalid, and the computed value of display on ::marker loses its list-item aspect.

4.3. Placeholder Input: the ::placeholder pseudo-element

::placeholder

In all current engines.

Firefox51+Safari10.1+Chrome57+
Opera44+Edge79+
Edge (Legacy)12+IENone
Firefox for Android51+iOS Safari10.3+Chrome for Android57+Android WebView57+Samsung Internet7.0+Opera Mobile43+

The ::placeholder pseudo-element represents placeholder text in an input field: text that represents the input and provides a hint to the user on how to fill out the form. For example, a date-input field might have the placeholder text “YYYY/MM/DD” to clarify that numeric dates are to be entered in year-month-day order.

Note: There also exists a :placeholder-shown pseudo-class, which applies to (real) elements while they are showing placeholder text, and can be used to style such elements specially. ::placeholder specifically selects a pseudo-element representing the placeholder text, and is thus relatively limited in its abilities.

All properties that apply to the ::first-line pseudo-element also apply to the ::placeholder pseudo-element.

In interactive media, placeholder text is often hidden once the user has entered input; however this is not a requirement, and both the input value and the placeholder text may be visible simultaneously. The exact behavior is UA-defined. Note that in static media (such as print) placeholder text will be present even after the user has entered input.

Authors seem to want text-align on the list of supported properties. See e.g. comments here.

Note: It’s been requested that ::placeholder also refer to a placeholder which has a corresponding element in the element tree. It’s not clear how this should work, but it may be worth doing. See Issue 2417.

4.4. File Selector Button: the ::file-selector-button pseudo-element

::file-selector-button

Firefox82+SafariNoneChrome89+
Opera75+Edge89+
Edge (Legacy)NoneIENone
Firefox for Android82+iOS SafariNoneChrome for Android89+Android WebView89+Samsung InternetNoneOpera MobileNone

The ::file-selector-button pseudo-element targets the <button> inside an <input> element with type=file, if the UA renders such a button.

There is no restriction on which properties apply to the ::file-selector-button pseudo-element.

For example, the following example should show a green border around the file selector button:
::file-selector-button { border: 3px solid green }

5. Overlapping Pseudo-element Interactions

Recall that

The following CSS and HTML example illustrates how overlapping pseudo-elements interact:

<style>
p { color: red; font-size: 12pt }
p::first-letter { color: green; font-size: 200% }
p::first-line { color: blue }
</style>

<p>Some text that ends up on two lines</p>

The first letter of each P element will be green with a font size of ’24pt'. The rest of the first formatted line will be blue while the rest of the paragraph will be red.

Assuming that a line break will occur before the word "ends", the fictional tag sequence for this fragment might be:

<p>
  <p::first-line>
    <p::first-letter>
      S
    </p::first-letter>
    ome text that
  </p::first-line>
  ends up on two lines
</p>

6. Additions to the CSS Object Model

6.1. CSSPseudoElement Interface

CSSPseudoElement

In only one current engine.

Firefox75+SafariNoneChromeNone
OperaNoneEdgeNone
Edge (Legacy)NoneIENone
Firefox for Android🔰 63–79iOS SafariNoneChrome for AndroidNoneAndroid WebViewNoneSamsung InternetNoneOpera MobileNone

The CSSPseudoElement interface allows pseudo-elements to be event targets.

[Exposed=Window]
interface CSSPseudoElement : EventTarget {
    readonly attribute CSSOMString type;
    readonly attribute Element element;
};

CSSPseudoElement/type

In only one current engine.

Firefox75+SafariNoneChromeNone
OperaNoneEdgeNone
Edge (Legacy)NoneIENone
Firefox for Android🔰 63–79iOS SafariNoneChrome for AndroidNoneAndroid WebViewNoneSamsung InternetNoneOpera MobileNone

The type attribute is a string representing the type of the pseudo-element. This can be one of the following values:

"::before"
Represents the ::before pseudo-element.
"::after"
Represents the ::after pseudo-element.
"::marker"
Represents the ::marker pseudo-element.

CSSPseudoElement/element

In only one current engine.

Firefox75+SafariNoneChromeNone
OperaNoneEdgeNone
Edge (Legacy)NoneIENone
Firefox for Android?iOS SafariNoneChrome for AndroidNoneAndroid WebViewNoneSamsung InternetNoneOpera MobileNone

The element attribute is the originating element of the pseudo-element.

Note: This interface may be extended in the future to other pseudo-element types and/or to allow setting style information through a CSSStyleDeclaration style attribute. The current functionality is limited to that which is needed to support [web-animations-1].

6.2. pseudo() method of the Element interface

A new method is added to the Element interface to retrieve pseudo-elements created by a given element for a given type:

partial interface Element {
  CSSPseudoElement? pseudo(CSSOMString type);
};
The pseudo(CSSOMString type) method is used to retrieve the CSSPseudoElement instance of the type matching type associated with the element. When it is called, execute the following steps:
  1. Parse the type argument as a <pseudo-element-selector>, and let type be the result.

  2. If type is failure, return null.

  3. Otherwise, return the CSSPseudoElement object representing the pseudo-element that would match the selector type with this as its originating element.

Return values that represent the same pseudo-element on the same originating element must be, insofar as observable, always the same CSSPseudoElement object. (The UA may drop or regenerate the object for convenience or performance if this is not observable.)

The identity, lifetime, and nullness of the return value (and potential error cases) of the pseudo() method is still under discussion. See Issue 3607 and Issue 3603.

7. Compatibility Syntax

For compatibility with existing style sheets written against CSS Level 2 [CSS2], user agents must also accept the previous one-colon notation (:before, :after, :first-letter, :first-line) for the ::before, ::after, ::first-letter, and ::first-line pseudo-elements.

Changes

Significant changes since the 25 February 2019 Working Draft include:

Changes since the 7 June 2016 Working Draft include:

Acknowledgements

The editors would like to specifically thank the following individuals for their contributions to this specification: Tab Atkins, David Baron, Oriol Brufau, Razvan Caliman, Chris Coyier, Anders Grimsrud, Vincent Hardy, François Remy.

Conformance

Document conventions

Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology. The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this document are to be interpreted as described in RFC 2119. However, for readability, these words do not appear in all uppercase letters in this specification.

All of the text of this specification is normative except sections explicitly marked as non-normative, examples, and notes. [RFC2119]

Examples in this specification are introduced with the words “for example” or are set apart from the normative text with class="example", like this:

This is an example of an informative example.

Informative notes begin with the word “Note” and are set apart from the normative text with class="note", like this:

Note, this is an informative note.

Advisements are normative sections styled to evoke special attention and are set apart from other normative text with <strong class="advisement">, like this: UAs MUST provide an accessible alternative.

Tests

Tests relating to the content of this specification may be documented in “Tests” blocks like this one. Any such block is non-normative.


Conformance classes

Conformance to this specification is defined for three conformance classes:

style sheet
A CSS style sheet.
renderer
A UA that interprets the semantics of a style sheet and renders documents that use them.
authoring tool
A UA that writes a style sheet.

A style sheet is conformant to this specification if all of its statements that use syntax defined in this module are valid according to the generic CSS grammar and the individual grammars of each feature defined in this module.

A renderer is conformant to this specification if, in addition to interpreting the style sheet as defined by the appropriate specifications, it supports all the features defined by this specification by parsing them correctly and rendering the document accordingly. However, the inability of a UA to correctly render a document due to limitations of the device does not make the UA non-conformant. (For example, a UA is not required to render color on a monochrome monitor.)

An authoring tool is conformant to this specification if it writes style sheets that are syntactically correct according to the generic CSS grammar and the individual grammars of each feature in this module, and meet all other conformance requirements of style sheets as described in this module.

Partial implementations

So that authors can exploit the forward-compatible parsing rules to assign fallback values, CSS renderers must treat as invalid (and ignore as appropriate) any at-rules, properties, property values, keywords, and other syntactic constructs for which they have no usable level of support. In particular, user agents must not selectively ignore unsupported component values and honor supported values in a single multi-value property declaration: if any value is considered invalid (as unsupported values must be), CSS requires that the entire declaration be ignored.

Implementations of Unstable and Proprietary Features

To avoid clashes with future stable CSS features, the CSSWG recommends following best practices for the implementation of unstable features and proprietary extensions to CSS.

Non-experimental implementations

Once a specification reaches the Candidate Recommendation stage, non-experimental implementations are possible, and implementors should release an unprefixed implementation of any CR-level feature they can demonstrate to be correctly implemented according to spec.

To establish and maintain the interoperability of CSS across implementations, the CSS Working Group requests that non-experimental CSS renderers submit an implementation report (and, if necessary, the testcases used for that implementation report) to the W3C before releasing an unprefixed implementation of any CSS features. Testcases submitted to W3C are subject to review and correction by the CSS Working Group.

Further information on submitting testcases and implementation reports can be found from on the CSS Working Group’s website at http://www.w3.org/Style/CSS/Test/. Questions should be directed to the public-css-testsuite@w3.org mailing list.

Index

Terms defined by this specification

Terms defined by reference

References

Normative References

[CSS-BACKGROUNDS-3]
Bert Bos; Elika Etemad; Brad Kemper. CSS Backgrounds and Borders Module Level 3. 22 December 2020. CR. URL: https://www.w3.org/TR/css-backgrounds-3/
[CSS-BREAK-4]
Rossen Atanassov; Elika Etemad. CSS Fragmentation Module Level 4. 18 December 2018. WD. URL: https://www.w3.org/TR/css-break-4/
[CSS-CASCADE-5]
Elika Etemad; Miriam Suzanne; Tab Atkins Jr.. CSS Cascading and Inheritance Level 5. 19 March 2021. WD. URL: https://www.w3.org/TR/css-cascade-5/
[CSS-COLOR-3]
Tantek Çelik; Chris Lilley; David Baron. CSS Color Module Level 3. 19 June 2018. REC. URL: https://www.w3.org/TR/css-color-3/
[CSS-COLOR-4]
Tab Atkins Jr.; Chris Lilley. CSS Color Module Level 4. 12 November 2020. WD. URL: https://www.w3.org/TR/css-color-4/
[CSS-CONTENT-3]
Elika Etemad; Dave Cramer. CSS Generated Content Module Level 3. 2 August 2019. WD. URL: https://www.w3.org/TR/css-content-3/
[CSS-DISPLAY-3]
Tab Atkins Jr.; Elika Etemad. CSS Display Module Level 3. 18 December 2020. CR. URL: https://www.w3.org/TR/css-display-3/
[CSS-INLINE-3]
Dave Cramer; Elika Etemad; Steve Zilles. CSS Inline Layout Module Level 3. 27 August 2020. WD. URL: https://www.w3.org/TR/css-inline-3/
[CSS-LISTS-3]
Elika Etemad; Tab Atkins Jr.. CSS Lists and Counters Module Level 3. 17 November 2020. WD. URL: https://www.w3.org/TR/css-lists-3/
[CSS-MULTICOL-1]
Håkon Wium Lie; Florian Rivoal; Rachel Andrew. CSS Multi-column Layout Module Level 1. 12 February 2021. WD. URL: https://www.w3.org/TR/css-multicol-1/
[CSS-RUBY-1]
Elika Etemad; et al. CSS Ruby Annotation Layout Module Level 1. 10 March 2021. WD. URL: https://www.w3.org/TR/css-ruby-1/
[CSS-SYNTAX-3]
Tab Atkins Jr.; Simon Sapin. CSS Syntax Module Level 3. 16 July 2019. CR. URL: https://www.w3.org/TR/css-syntax-3/
[CSS-TABLES-3]
François Remy; Greg Whitworth; David Baron. CSS Table Module Level 3. 27 July 2019. WD. URL: https://www.w3.org/TR/css-tables-3/
[CSS-TEXT-3]
Elika Etemad; Koji Ishii; Florian Rivoal. CSS Text Module Level 3. 22 April 2021. CR. URL: https://www.w3.org/TR/css-text-3/
[CSS-TEXT-DECOR-4]
Elika Etemad; Koji Ishii. CSS Text Decoration Module Level 4. 6 May 2020. WD. URL: https://www.w3.org/TR/css-text-decor-4/
[CSS-UI-4]
Florian Rivoal. CSS Basic User Interface Module Level 4. 16 March 2021. WD. URL: https://www.w3.org/TR/css-ui-4/
[CSS-VARIABLES-1]
Tab Atkins Jr.. CSS Custom Properties for Cascading Variables Module Level 1. 3 December 2015. CR. URL: https://www.w3.org/TR/css-variables-1/
[CSS-WRITING-MODES-3]
Elika Etemad; Koji Ishii. CSS Writing Modes Level 3. 10 December 2019. REC. URL: https://www.w3.org/TR/css-writing-modes-3/
[CSS-WRITING-MODES-4]
Elika Etemad; Koji Ishii. CSS Writing Modes Level 4. 30 July 2019. CR. URL: https://www.w3.org/TR/css-writing-modes-4/
[CSS2]
Bert Bos; et al. Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification. 7 June 2011. REC. URL: https://www.w3.org/TR/CSS21/
[CSSOM-1]
Simon Pieters; Glenn Adams. CSS Object Model (CSSOM). 17 March 2016. WD. URL: https://www.w3.org/TR/cssom-1/
[DOM]
Anne van Kesteren. DOM Standard. Living Standard. URL: https://dom.spec.whatwg.org/
[FILL-STROKE-3]
Elika Etemad; Tab Atkins Jr.. CSS Fill and Stroke Module Level 3. 13 April 2017. WD. URL: https://www.w3.org/TR/fill-stroke-3/
[RFC2119]
S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. March 1997. Best Current Practice. URL: https://tools.ietf.org/html/rfc2119
[SELECTORS-4]
Elika Etemad; Tab Atkins Jr.. Selectors Level 4. 21 November 2018. WD. URL: https://www.w3.org/TR/selectors-4/
[UAX44]
Ken Whistler; Laurențiu Iancu. Unicode Character Database. 4 March 2020. Unicode Standard Annex #44. URL: https://www.unicode.org/reports/tr44/tr44-26.html
[URL]
Anne van Kesteren. URL Standard. Living Standard. URL: https://url.spec.whatwg.org/
[WebIDL]
Boris Zbarsky. Web IDL. 15 December 2016. ED. URL: https://heycam.github.io/webidl/

Informative References

[CSS-CASCADE-4]
Elika Etemad; Tab Atkins Jr.. CSS Cascading and Inheritance Level 4. 19 March 2021. WD. URL: https://www.w3.org/TR/css-cascade-4/
[CSS-FONTS-3]
John Daggett; Myles Maxfield; Chris Lilley. CSS Fonts Module Level 3. 20 September 2018. REC. URL: https://www.w3.org/TR/css-fonts-3/
[CSS-TEXT-DECOR-3]
Elika Etemad; Koji Ishii. CSS Text Decoration Module Level 3. 13 August 2019. CR. URL: https://www.w3.org/TR/css-text-decor-3/
[HTML5]
Ian Hickson; et al. HTML5. 27 March 2018. REC. URL: https://www.w3.org/TR/html5/
[SELECTORS-3]
Tantek Çelik; et al. Selectors Level 3. 6 November 2018. REC. URL: https://www.w3.org/TR/selectors-3/
[UAX29]
Mark Davis; Christopher Chapman. Unicode Text Segmentation. 19 February 2020. Unicode Standard Annex #29. URL: https://www.unicode.org/reports/tr29/tr29-37.html
[WEB-ANIMATIONS-1]
Brian Birtles; et al. Web Animations. 11 October 2018. WD. URL: https://www.w3.org/TR/web-animations-1/

IDL Index

[Exposed=Window]
interface CSSPseudoElement : EventTarget {
    readonly attribute CSSOMString type;
    readonly attribute Element element;
};

partial interface Element {
  CSSPseudoElement? pseudo(CSSOMString type);
};

Issues Index

Are there any other properties that should be included here?
See F2F minutes, dbaron’s message, Daniel’s thread, Gecko notes, Opera notes, Webkit notes
Not sure if this is the correct way of describing the way things work.
Interaction of ::marker and ::first-line is currently under discussion in Issue 4506.
Authors seem to want text-align on the list of supported properties. See e.g. comments here.
The identity, lifetime, and nullness of the return value (and potential error cases) of the pseudo() method is still under discussion. See Issue 3607 and Issue 3603.