CSS Lists and Counters Module Level 3

1. Introduction

This specification defines the ::marker pseudo-element, the list-item display type that generates markers, and several properties controlling the placement and styling of markers.

It also defines counters, which are special numerical objects often used to generate the default contents of markers.

<style>
li::marker { content: "(" counter(list-item, lower-roman) ")"; }
li { display: list-item; }
</style>
<ol>
  <li>This is the first item.
  <li>This is the second item.
  <li>This is the third item.
</ol>

  (i) This is the first item.
 (ii) This is the second item.
(iii) This is the third item.

With descendant selectors and child selectors, it’s possible to specify different marker types depending on the depth of embedded lists.

1.1. Value Definitions

This specification follows the CSS property definition conventions from [CSS2] using the value definition syntax from [CSS-VALUES-3]. Value types not defined in this specification are defined in CSS Values & Units [CSS-VALUES-3]. Combination with other CSS modules may expand the definitions of these value types.

In addition to the property-specific values listed in their definitions, all properties defined in this specification also accept the CSS-wide keywords as their property value. For readability they have not been repeated explicitly.

2. Declaring a List Item

A list item is any element with its display property set to list-item. List items generate ::marker pseudo-elements; no other elements do. Additionally, list items automatically increment an implied list-item counter (see § 4.6 The Implicit list-item Counter).

3. Markers

The defining feature of the list item display type is its marker, a symbol or ordinal that helps denote the beginning of each list item in a list. In the CSS layout model, list item markers are represented by a marker box associated with each list item. The contents of this marker can be controlled with the list-style-type and list-style-image properties on the list item and by assigning properties to its ::marker pseudo-element.

3.1. The ::marker Pseudo-Element

The marker box is generated by the ::marker pseudo-element of a list item as the list item’s first child, before the ::before pseudo-element (if it exists on the element). It is filled with content as defined in § 3.2 Generating Marker Contents.

<style>
p { margin-left: 12 em; }
p.note {
  display: list-item;
  counter-increment: note-counter;
}
p.note::marker {
  content: "Note " counter(note-counter) ":";
}
</style>
<p>This is the first paragraph in this document.
<p class="note">This is a very short document.
<p>This is the end.

        This is the first paragraph
        in this document.

Note 1: This is a very short
        document.

        This is the end.

<style>
p { margin-left: 8em } /* Make space for counters */
li { list-style-type: lower-roman; }
li::marker { color: blue; font-weight:bold; }
</style>
<p>This is a long preceding paragraph ...
<ol>
  <li>This is the first item.
  <li>This is the second item.
  <li>This is the third item.
</ol>
<p>This is a long following paragraph ...

       This is a long preceding
       paragraph ...

  i.   This is the first item.
 ii.   This is the second item.
iii.   This is the third item.

       This is a long following
       paragraph ...

Marker boxes only exist for list items: on any other element, the ::marker pseudo-element’s content property must compute to none, which suppresses its creation.

3.1.1. Properties Applying to ::marker

All properties can be set on a ::marker pseudo-element and will have a computed value which will then inherit to its text content.

However, only the following CSS properties actually apply to a marker box:

• the text-combine-upright, unicode-bidi, and direction properties (see [CSS-WRITING-MODES-3])
• the content property (see § 3.2 Generating Marker Contents, below)
• all animation and transition properties (see [CSS-ANIMATIONS-1] and [CSS-TRANSITIONS-1])

Other properties should not have an effect on the marker box when declared directly on ::marker in the author or user origin of the cascade. UAs may either treat such properties as not applying, or enforce their value or inheritance from the originating element by setting a user-agent origin !important rule.

NOTE: It is expected that future specifications will extend this list of properties and relax the restriction on which properties can take effect. However at the moment outside marker box layout is not fully defined, so to avoid future compatibility problems only these properties are allowed.

Additionally, UAs must add the following rule to their default style sheet:

::marker, ::before::marker, ::after::marker {
  unicode-bidi: isolate;
  font-variant-numeric: tabular-nums;
  white-space: pre;
  text-transform: none;
}

white-space: pre doesn’t have quite the right behavior; text-space-collapse: preserve-spaces + text-space-trim: discard-after might be closer to what’s needed here. See discussion in Issue 4448 and Issue 4891.

Note: Although the ::marker pseudo-element can represent the marker box of a ::before or ::after pseudo-element, the compound selector ::marker, which expands to *::marker [SELECTORS-4], will not select these markers—an originating element that is a pseudo-element needs to be explicitly specified in the selector, e.g. ::before::marker.

3.2. Generating Marker Contents

The contents of a marker box are determined by the first of these conditions that is true:

content on the ::marker itself is not normal

The contents of the marker box are determined as defined by the content property, exactly as for ::before.

list-style-image on the originating element defines a marker image

The marker box contains an anonymous inline replaced element representing the specified marker image, followed by a text run consisting of a single space (U+0020 SPACE).

list-style-type on the originating element defines a marker string

The marker box contains a text run consisting of the specified marker string.

otherwise

The marker box has no contents and ::marker does not generate a box.

Additionally, the UA may transform into spaces or discard any preserved forced line breaks.

3.3. Image Markers: the list-style-image property

Specifies the marker image, which is used to fill the list item’s marker when its content is normal. The values are as follows:

<image>

If the <image> represents a valid image, specifies the element’s marker image as the <image>. Otherwise, the element has no marker image.

none

The element has no marker image.

The marker image is sized using the default sizing algorithm [css-images-3] with no specified size and a default object size of 1em square.

li { list-style-image: url("http://www.example.com/ellipse.png") }

3.4. Text-based Markers: the list-style-type property

Specifies the marker string, which is used to fill the list item’s marker when its content value is normal and there is no marker image. The values are as follows:

<counter-style>

Specifies the element’s marker string as the value of the list-item counter represented using the specified <counter-style>.

Specifically, the marker string is the result of generating a counter representation of the list-item counter value using the specified <counter-style>, prefixed by the prefix of the <counter-style>, and followed by the suffix of the <counter-style>. If the specified <counter-style> does not exist, decimal is assumed.

<string>

The element’s marker string is the specified <string>.

none

The element has no marker string.

ul { list-style-type: "★"; }
/* Sets the marker to a "star" character */

p.note {
  display: list-item;
  list-style-type: "Note: ";
  list-style-position: inside;
}
/* Gives note paragraphs a marker consisting of the string "Note: " */

ol { list-style-type: upper-roman; }
/* Sets all ordered lists to use the upper-roman counter-style
   (defined in the Counter Styles specification [[CSS-COUNTER-STYLES]]) */

ul { list-style-type: symbols(cyclic '○' '●'); }
/* Sets all unordered list items to alternate between empty and
   filled circles for their markers. */

ul { list-style-type: none; }
/* Suppresses the marker entirely, unless list-style-image is specified
   with a valid image. */

3.5. Positioning Markers: The list-style-position property

This property dictates whether the ::marker is rendered inline, or positioned just outside of the list item. The values are as follows:

inside

No special effect. (The ::marker is an inline element at the start of the list item’s contents.)

outside

If the list item is a block container: the marker box is a block container and is placed outside the principal block box; however, the position of the list-item marker adjacent to floats is undefined. CSS does not specify the precise location of the marker box or its position in the painting order, but does require that it be placed on the inline-start side of the box, using the writing mode of the box indicated by marker-side. The marker box is fixed with respect to the principal block box’s border and does not scroll with the principal box’s content. A UA may hide the marker if the element’s overflow is other than visible. (This allowance may change in the future.) The size or contents of the marker box may affect the height of the principal block box and/or the height of its first line box, and in some cases may cause the creation of a new line box; this interaction is also not defined.

This is handwavey nonsense from CSS2, and needs a real definition.

If the list item is an inline box: this value is equivalent to inside.

Alternatively, outside could lay out the marker as a previous sibling of the principal inline box.

<style>
  ul.compact { list-style: inside; }
  ul         { list-style: outside; }
</style>
<ul class=compact>
  <li>first "inside" list item comes first</li>
  <li>second "inside" list item comes first</li>
</ul>
<hr>
<ul>
  <li>first "outside" list item comes first</li>
  <li>second "outside" list item comes first</li>
</ul>

  * first "inside" list
  item comes first
  * second "inside" list
  item comes second

========================

* first "outside" list
  item comes first
* second "outside" list
  item comes second

3.6. Styling Markers: the list-style shorthand property

The list-style property is a shorthand notation for setting the three properties list-style-type, list-style-image, and list-style-position at the same place in the style sheet.

ul { list-style: upper-roman inside }  /* Any UL */
ul ul { list-style: circle outside } /* Any UL child of a UL */

Using a value of none in the shorthand is potentially ambiguous, as none is a valid value for both list-style-image and list-style-type. To resolve this ambiguity, a value of none in the shorthand must be applied to whichever of the two properties aren’t otherwise set by the shorthand.

list-style: none disc;
/* Sets the image to "none" and the type to "disc". */

list-style: none url(bullet.png);
/* Sets the image to "url(bullet.png)" and the type to "none". */

list-style: none;
/* Sets both image and type to "none". */

list-style: none disc url(bullet.png);
/* Syntax error */

Note: The <counter-style> values of list-style-type can also create grammatical ambiguities. As such values are ultimately <custom-ident> values, the parsing rules in [CSS-VALUES-3] apply.

ol.alpha li { list-style: lower-alpha; }
ul li       { list-style: disc; }

ol.alpha > li { list-style: lower-alpha; }
ul > li       { list-style: disc; }

ol.alpha { list-style: lower-alpha; }
ul       { list-style: disc; }

3.7. The marker-side property

The marker-side property specifies whether an outside marker box is positioned based on the directionality of the list item itself (i.e. its originating element) or the directionality of the list container (i.e. the originating element’s parent). In the first case, the position of the marker can vary across items in the same list, based on the directionality assigned to each list item individually; in the second case they will all align on the same side, as determined by the directionality assigned to the list as a whole.

match-self

The marker box is positioned using the directionality of the ::marker’s originating element.

match-parent

The marker box is positioned using the directionality of the ::marker’s originating element’s parent element.

<ul>
  <li>english one
  <li dir=rtl>OWT WERBEH
  <li>english three
  <li dir=rtl>RUOF WERBEH
</ul>

* english one
     OWT WERBEH *
* english three
    RUOF WERBEH *

* english one
*    OWT WERBEH
* english three
*   RUOF WERBEH

For this order punctuation inside the marker correctly, it would also need to take the direction value of the parent. [Issue #4202]

There are issues open on renaming the keywords and on merging with list-style-position.

4. Automatic Numbering With Counters

A counter is a special numeric tracker used, among other things, to automatically number list items in CSS. Every element has a collection of zero or more counters, which are inherited through the document tree in a way similar to inherited property values. Counters have a name and creator, which identify the counter, a boolean reversed (false by default), and an integer value (optional when the counter is reversed). They are created and manipulated with the counter properties counter-increment, counter-set and counter-reset, and used with the counter() and counters() functional notations.

Counters are referred to in CSS syntax using the <counter-name> type, which represents their name as a <custom-ident>. A <counter-name> name cannot match the keyword none; such an identifier is invalid as a <counter-name>.

A reversed counter is created with the reversed() functional notation, which is defined as follows:

<reversed-counter-name> = reversed( <counter-name> )

Resolving counter values on a given element is a multi-step process:

1. Existing counters are inherited from previous elements.

2. New counters are instantiated (counter-reset).

3. Counter values are incremented (counter-increment).

4. Counter values are explicitly set (counter-set).

5. Counter values are used (counter()/counters()).

UAs may have implementation-specific limits on the maximum or minimum value of a counter. If a counter reset, set, or increment would push the value outside of that range, the value must be clamped to that range.

4.1. Creating Counters: the counter-reset property

User agents are expected to support this property on all media, including non-visual ones.

The counter-reset property instantiates new counters on an element and sets them to the specified integer values. Its values are defined as follows:

none

This element does not create any new counters.

<counter-name> <integer>?

Instantiates a counter of the given <counter-name> with a starting value of the given <integer>, defaulting to 0.

<reversed-counter-name> <integer>?

Instantiates a reversed counter of the given <counter-name> with a starting value of the given <integer>, or no starting value if not given.

h1 { counter-reset: section -1 }
h1 { counter-reset: imagenum 99 }

H1 { counter-reset: section -1 imagenum 99 }

If multiple instances of the same <counter-name> occur in the property value, only the last one is honored.

4.2. Manipulating Counter Values: the counter-increment and counter-set properties

User agents are expected to support this property on all media, including non-visual ones.

User agents are expected to support this property on all media, including non-visual ones.

The counter-increment and counter-set properties manipulate the value of existing counters. They only instantiate new counters if there is no counter of the given name on the element yet. Their values are defined as follows:

none

This element does not alter the value of any counters.

<counter-name> <integer>?

Sets (for counter-set) or increments (for counter-increment) the value of the named counter on the element to/by the specified <integer>. If the <integer> is omitted, it defaults to 1 (for counter-increment) or 0 (for counter-set).

If there is not currently a counter of the given name on the element, the element instantiates a new counter of the given name with a starting value of 0 before setting or incrementing its value.

h1::before {
    content: "Chapter " counter(chapter) ". ";
    counter-increment: chapter;  /* Add 1 to chapter */
    counter-reset: section;      /* Set section to 0 */
}
h2::before {
    content: counter(chapter) "." counter(section) " ";
    counter-increment: section;
}

If multiple instances of the same <counter-name> occur in the property value, they are all processed, in order. Thus increments will compound, but only the last set value will take effect.

4.3. Nested Counters and Scope

Counters are “self-nesting”; instantiating a new counter on an element which inherited an identically-named counter from its parent creates a new counter of the same name, nested inside the existing counter. This is important for situations like lists in HTML, where lists can be nested inside lists to arbitrary depth: it would be impossible to define uniquely named counters for each level. The counter() function only retrieves the innermost counter of a given name on the element, whereas the counters() function uses all counters of a given name that contain the element.

The scope of a counter therefore starts at the first element in the document that instantiates that counter and includes the element’s descendants and its following siblings with their descendants. However, it does not include any elements in the scope of a counter with the same name created by a counter-reset on a later sibling of the element, allowing such explicit counter instantiations to obscure those earlier siblings.

See § 4.4 Creating and Inheriting Counters for the exact rules governing the scope of counters and their values.

ol { counter-reset: item }
li { display: block }
li::before { content: counter(item) ". "; counter-increment: item }

4.4. Creating and Inheriting Counters

Each element or pseudo-element in a document has a (possibly empty) set of counters in the scope of that element, either through inheritance from another element or through instantiation on the element directly. These counters are represented as a CSS counters set, which is a set whose values are each a tuple of: a string (representing a counter’s name), an element (representing the counter’s creator), a boolean (representing whether the counter is reversed), and optionally an integer (representing the counter’s value). The latest counter of a given name in that set represents the innermost counter of that name.

4.4.1. Inheriting Counters

<ul style='counter-reset: example 0;'>
  <li id='foo' style='counter-increment: example;'>
    foo
    <div id='bar' style='counter-increment: example;'>bar</div>
  </li>
  <li id='baz'>
    baz
  </li>
</ul>

Note: Counter inheritance, like regular CSS inheritance, operates on the “flattened element tree” in the context of the [DOM].

4.4.2. Instantiating Counters

When a counter is instantiated without an initial value, the user agent must dynamically calculate the initial value at layout-time to be the value returned by the following algorithm:

1. Let num be 0.

2. Let first be true.

3. For each element or pseudo-element el that increments or sets the same counter in the same scope:

   1. Let incrementNegated be el’s counter-increment integer value for this counter, multiplied by -1.

   2. If first is true, then add incrementNegated to num and set first to false.

   3. If el sets this counter with counter-set, then add that integer value to num and break this loop.

   4. Add incrementNegated to num.

4. Return num.

Note: Only reversed counters can be instantiated without an initial value.

4.5. Counters in elements that do not generate boxes

An element that does not generate a box (for example, an element with display set to none, or a pseudo-element with content set to none) cannot set, reset, or increment a counter. The counter properties are still valid on such an element, but they must have no effect.

h2 { counter-increment: count2; }
h2.secret { display: none; }

Note: Other methods of “hiding” elements, such as setting visibility to hidden, still cause the element to generate a box, and so are not excepted here.

Whether a replaced element’s descendants (such as HTML option, or SVG rect) can set, reset, or increment a counter is undefined.

Note: The behavior on replaced element descendants is currently undefined due to a lack of interoperability across implementations.

4.6. The Implicit list-item Counter

In addition to any explicitly defined counters that authors write in their styles, list items automatically increment a special list-item counter, which is used when generating the default marker string on list items (see list-style-type).

Specifically, unless the counter-increment property explicitly specifies a different increment for the list-item counter, it must be incremented by 1 on every list item, or if the counter is reversed, it must be incremented by -1 on every list item instead, at the same time that counters are normally incremented (exactly as if the list item had list-item 1 or list-item -1 appended to their counter-increment value, including side-effects such as possibly instantiating a new counter, etc). This does not affect the specified or computed values of counter-increment.

In all other respects, the list-item counter behaves like any other counter and can be used and manipulated by authors to adjust list item styling or for other purposes.

ol.evens > li { counter-increment: list-item 2; }

2. First Item
4. Second Item
6. Third Item

UAs and host languages should ensure that the list-item counter values by default reflect the underlying numeric value dictated by host language semantics when setting up list item styling in their UA style sheet and presentational hint style mappings. See, e.g. Appendix A: Sample Style Sheet For HTML.

ol > li::marker { content: counters(list-item,'.') '.'; }

1. First top-level item
5. Second top-level item, value=5
   5.3. First second-level item, list start=3
   5.4. Second second-level item, list start=3
        5.4.4. First third-level item in reversed list
        5.4.3. Second third-level item in reversed list
        5.4.2. Third third-level item in reversed list
        5.4.1. Fourth third-level item in reversed list
   5.5. Third second-level item, list start=3
6. Third top-level item

<ol>
  <li>First top-level item
  <li value=5>Second top-level item, value=5
    <ol start=3>
      <li>First second-level item, list start=3
      <li>Second second-level item, list start=3
        <ol reversed>
          <li>First third-level item in reversed list
          <li>Second third-level item in reversed list
          <li>Third third-level item in reversed list
          <li>Fourth third-level item in reversed list
        </ol>
    </ol>
  <li>Third second-level item, list start=3
  <li>Third top-level item
</ol>

4.7. Outputting Counters: the counter() and counters() functions

Counters have no visible effect by themselves, but their values can be used with the counter() and counters() functions, whose used values represent counter values as strings or images. They are defined as follows:

<counter> = <counter()> | <counters()>
counter()  =  counter( <counter-name>, <counter-style>? )
counters() = counters( <counter-name>, <string>, <counter-style>? )

where <counter-style> specifies the counter style for generating a representation of the named counter(s) as defined in [css-counter-styles-3] and

counter()

Represents the value of the innermost counter in the element’s CSS counters set named <counter-name> using the counter style named <counter-style>.

counters()

Represents the values of all the counters in the element’s CSS counters set named <counter-name> using the counter style named <counter-style>, sorted in outermost-first to innermost-last order and joined by the specified <string>.

In both cases, if the <counter-style> argument is omitted it defaults to decimal.

Note: If the <counter-style> is one of the predefined symbolic styles, like disc, it might look different than when used in list-style-type. See CSS Counter Styles 3 § 6.3 Symbolic: disc, circle, square, disclosure-open, disclosure-closed.

If no counter named <counter-name> exists on an element where counter() or counters() is used, one is first instantiated with a starting value of 0.

H1::before        { content: counter(chno, upper-latin) ". " }
/* Generates headings like "A. A History of Discontent" */

H2::before        { content: counter(section, upper-roman) " - " }
/* Generates headings like "II - The Discontent Part" */

BLOCKQUOTE::after { content: " [" counter(bq, decimal) "]" }
/* Generates blockquotes that end like "... [3]" */

DIV.note::before  { content: counter(notecntr, disc) " " }
/* Simply generates a bullet before every div.note */

P::before         { content: counter(p, none) }
/* inserts nothing */

<ul>
  <li>one</li>
  <li>two
    <ul>
      <li>nested one</li>
      <li>nested two</li>
    </ul>
  </li>
  <li>three</li>
</ul>
<style>
li::marker { content: '(' counters(list-item,'.') ') '; }
</style>

(1) one
(2) two
   (2.1) nested one
   (2.2) nested two
(3) three

<h1>First H1</h1>
...
<h2>First H2 in H1</h2>
...
<h2>Second H2 in H1</h2>
...
<h3>First H3 in H2</h3>
...
<h1>Second H1</h1>
...
<h2>First H2 in H1</h2>
...
<style>
body { counter-reset: h1 h2 h3; }
h1   { counter-increment: h1; counter-reset: h2 h3;}
h2   { counter-increment: h2; counter-reset:    h3; }
h3   { counter-increment: h3; }
h1::before { content: counter(h1,upper-alpha) ' '; }
h2::before { content: counter(h1,upper-alpha) '.'
                      counter(h2,decimal) ' '; }
h3::before { content: counter(h1,upper-alpha) '.'
                      counter(h2,decimal) '.'
                      counter(h3,lower-roman) ' '; }
</style>

A First H1
...
A.1 First H2 in H1
...
A.2 Second H2 in H1
...
A.2.i First H3 in H2
...
B Second H1
...
B.1 First H2 in H1
...

Appendix A: Sample Style Sheet For HTML

This section is informative, not normative. The [HTML] Rendering chapter defines the normative default properties that apply to HTML lists; this sample style sheet is provided to illustrate the CSS features using familiar markup conventions.

/* Set up list items */
li {
  display: list-item; /* implies 'counter-increment: list-item' */
}

/* Set up ol and ul so that they scope the list-item counter */
ol, ul {
  counter-reset: list-item;
}

/* Default list style types for lists */
ol { list-style-type: decimal; }
ul { list-style-type: toggle(disc, circle, square); }

/* The type attribute on ol and ul elements */
ul[type="disc"]   { list-style-type: disc;   }
ul[type="circle"] { list-style-type: circle; }
ul[type="square"] { list-style-type: square; }
ol[type="1"] { list-style-type: decimal;     }
ol[type="a"] { list-style-type: lower-alpha; }
ol[type="A"] { list-style-type: upper-alpha; }
ol[type="i"] { list-style-type: lower-roman; }
ol[type="I"] { list-style-type: upper-roman; }

/* The start attribute on ol elements */
ol[start] {
  counter-reset: list-item calc(attr(start integer, 1) - 1);
}

/* The value attribute on li elements */
li[value] {
  counter-set: list-item attr(value integer, 1);
}

/* Handling reversed lists */
ol[reversed] {
  counter-reset: reversed(list-item);
}
ol[reversed][start] {
  counter-reset: reversed(list-item) calc(attr(start integer) + 1);
}

/* Box Model Rules */
ol, ul {
  display: block;
  margin-block: 1em;
  marker-side: match-parent;
  padding-inline-start: 40px;
}
ol ol, ol ul, ul ul, ul ol {
  margin-block: 0;
}

li {
  text-align: match-parent;
}

Acknowledgments

This specification is made possible by input from Aharon Lanin, Arron Eicholz, Brad Kemper, David Baron, Emilio Cobos Álvarez, Mats Palmgren, Oriol Brufau, Simon Sapin, Xidorn Quan

Changes

This section documents the changes since previous publications.

Changes since the 9 July 2020 WD

• Clarified properties that apply to ::marker boxes vs. to the contents of ::marker boxes. (Issue 4568)
• Added text-transform: none to the UA default style sheet for ::marker. (Issue 4206)
• Changed counter inheritance to take from the parent first, and only take from the sibling if it’s a new counter. (Issue 5477)

Changes since the 17 August 2019 WD

• Specified that outside list markers block containers. (Their outer display type remains undefined.)
• Stole list of properties applying to ::marker from [CSS-PSEUDO-4] and added animations, transitions, and white-space.
• Added white-space: pre to UA default style sheet for ::marker. (Issue 4448) Note, however, that the exact white space processing behavior of marker boxes is still being worked out.

Changes since the 25 April 2019 WD

• Rewrote the § 4 Automatic Numbering With Counters section for better precision, editorial clarity, and synchronization with CSS2.

Changes since the 20 March 2014 WD

• Use <custom-ident> consistently for counter names.
• Dropped position: marker (marker positioning is now mostly undefined, as in CSS2).
• Completely rewrote chapter on markers to tighten it up, align with current expectations, and make editorial improvements.
• Pulled the list-item counter definition into its own section, added examples, and made some clarifications.
• Renamed values of marker-side to match conventions from box/text alignment.
• Defined that counter-set is applied after counter-increment rather than before. (Issue 3810)
• Established the canonical order of list-style serialization to put <'list-style-type'> last. (Issue 2624)

Changes From CSS Level 2

As described in the introduction section, there are significant changes in this module when compared to CSS2.1.

1. The ::marker pseudo-element has been introduced to allow styling of the list marker directly.
2. list-style-type now accepts a <string> as well as the extended <counter-style> values from [css-counter-styles-3]..
3. The list-item predefined counter identifier has been introduced.
4. The counter-set property has been added.
5. Allowed for inline-level list items, as introduced in [CSS-DISPLAY-3].