system
The system
descriptor specifies the algorithm to be used for converting the integer value of a counter to a string representation. It is used in a @counter-style
to define the behavior of the defined style.
If the algorithm specified in the system
descriptor is unable to construct the representation for a particular counter value, then that value's representation will be constructed using the fallback system provided.
Syntax
css
/* Keyword values */
system: cyclic;
system: numeric;
system: alphabetic;
system: symbolic;
system: additive;
system: fixed;
/* Combined values */
system: fixed 3;
system: extends decimal;
This may take one of three forms:
- One of the keyword values
cyclic
,numeric
,alphabetic
,symbolic
,additive
, orfixed
. - The keyword value
fixed
along with an integer. - The keyword value or
extends
along with a@counter-style
name.
cyclic
-
Cycles through the list of symbols provided. Once the end of the list of symbols is reached, it will loop back to the beginning and start over. This system is useful for simple bullet styles with just one symbol, or for styles having multiple symbols. At least one symbol must be specified in the
symbols
descriptor, or the counter style is not valid. fixed
-
Defines a finite set of symbols are specified. Once the system has looped through all the specified symbols, it will fall back. This system is useful in cases where the counter values are finite. At least one symbol must be specified in the
symbols
descriptor or the counter style is not valid. Also an optional<integer>
can be specified after the system, as the value of the first symbol. If this integer is omitted, value of the first integer is taken as1
. symbolic
-
Cycles through the provided list of symbols. On each successive pass through the cycle, the symbols used for the counter representation are doubled, tripled, and so on. For example, if the original symbols provided were "◽" and "◾", on each successive pass, they will become "◽◽" and "◾◾", "◽◽◽" and "◾◾◾" and so on. At least one symbol must be specified in the
symbols
descriptor or the counter style is not valid. This counter system works for positive counter values only. alphabetic
-
Interprets the specified symbols as digits, to an alphabetic numbering system. If the characters
"a"
to"z"
are specified as symbols in a counter style, with thealphabetic
system, then the first 26 counter representations will be"a"
,"b"
up to"z"
. Until this point, the behavior is the same as that of thesymbolic
system, described above. However, after"z"
, it will continue as"aa"
,"ab"
,"ac"
…The
symbols
descriptor must contain at least two symbols or the counter style is not valid. The first counter symbol provided in thesymbols
descriptor is interpreted as1
, the next as2
, and so on. This system is also defined strictly over positive counter values. numeric
-
Interprets the counter symbols as digits in a place-value numbering system. The numeric system is similar to the
alphabetic
system, described above. The main difference is that in thealphabetic
system, the first counter symbol given in thesymbols
descriptor is interpreted as1
, the next as2
, and so on. However, in the numeric system, the first counter symbol is interpreted as 0, the next as1
, then2
, and so on.At least two counter symbols must be specified in the
symbols
descriptor or the counter style is not valid. additive
-
Used to represent "sign-value" numbering systems, such as Roman numerals, which rather than reuse digits in different positions to obtain different values, define additional digits for larger values. The value of a number in such a system can be found out by adding the digits in the number.
An additional descriptor called
additive-symbols
must be specified with at least one additive tuple, or else the counter style rule will not be valid. An additive tuple is similar to a composite counter symbol, which is made up of two parts: a normal counter symbol and a non-negative integer weight. The additive tuples must be specified in the descending order of their weights or the system is invalid. extends
-
Allows authors to use the algorithm of another counter style, but alter its other aspects. If a counter style rule is using the
extends
system, any unspecified descriptors, and their values will be taken from the extended counter style specified. If the specified counter style name in extends, is not a currently defined counter style name, it will instead extend from the decimal counter style.It must not contain a
symbols
oradditive-symbols
descriptor, or else the counter style rule is invalid. If one or more counter styles definitions form a cycle with their extends values, the browser will treat all the participating counter styles as extending from the decimal style.
Formal definition
Related at-rule | @counter-style |
---|---|
Initial value | symbolic |
Computed value | as specified |
Formal syntax
Examples
Cyclic counter
If your browser supports it, this example will render a list like this:
◉ One ◉ Two ◉ Three
CSS
css
@counter-style fisheye {
system: cyclic;
symbols: ◉;
suffix: " ";
}
ul {
list-style: fisheye;
}
Result
Fixed counter
If your browser supports it, this example will render a list like this:
➀ One ➁ Two ➂ Three 4 Four 5 Five
CSS
css
@counter-style circled-digits {
system: fixed;
symbols: ➀ ➁ ➂;
suffix: " ";
}
ul {
list-style: circled-digits;
}
Result
Symbolic counter
If your browser supports it, this example will render a list like this:
a. One b. Two c. Three aa. Four bb. Five cc. Six aaa. Seven bbb. Eight
CSS
css
@counter-style abc {
system: symbolic;
symbols: a b c;
suffix: ". ";
}
ul {
list-style: abc;
}
Result
Alphabetic counter
If your browser supports it, this example will render a list like this:
a. One b. Two c. Three aa. Four ab. Five ac. Six ba. Seven bb. Seven
CSS
css
@counter-style abc {
system: alphabetic;
symbols: a b c;
suffix: ". ";
}
ul {
list-style: abc;
}
Result
Numeric counter
If your browser supports it, this example will render a list like this:
b. One c. Two ba. Three bb. Four bc. Five ca. Six cb. Seven cc. Eight
The first symbol provided in the symbols
descriptor is interpreted as 0
here.
CSS
css
@counter-style abc {
system: numeric;
symbols: a b c;
suffix: ". ";
}
ul {
list-style: abc;
}
Result
Numeric counter with numeric symbols
As shown in the following example, if digits from 0
to 9
are specified as symbols, this counter style will render symbols same as the decimal counter style.
CSS
css
@counter-style numbers {
system: numeric;
symbols: "0" "1" "2" "3" "4" "5" "6" "7" "8" "9";
suffix: ".";
}
ul {
list-style: numbers;
}
Result
Additive counter
This example renders a list using Roman numerals. Notice that a range
is specified. This is because the representation will produce correct Roman numerals only until the counter value of 3999
. Once outside of the range, the rest of the counter representations will be based on the decimal
style, which is the fall back. If you need to represent counter values as Roman numerals, you could use either one of the predefined counter styles, upper-roman
or lower-roman
, rather than recreating the rule yourself.
HTML
html
<ul class="list">
<li>One</li>
<li>Two</li>
<li>Three</li>
<li>Four</li>
<li>Five</li>
</ul>
CSS
css
@counter-style upper-roman {
system: additive;
range: 1 3999;
additive-symbols: 1000 M, 900 CM, 500 D, 400 CD, 100 C, 90 XC, 50 L, 40 XL,
10 X, 9 IX, 5 V, 4 IV, 1 I;
}
ul {
list-style: upper-roman;
}
Result
Extends example
This example will use the algorithm, symbols, and other properties of the lower-alpha
counter style, but will remove the period ('.'
) after the counter representation, and enclose the characters in parenthesis; like (a)
, (b)
, etc.
HTML
html
<ul class="list">
<li>One</li>
<li>Two</li>
<li>Three</li>
<li>Four</li>
<li>Five</li>
</ul>
CSS
css
@counter-style alpha-modified {
system: extends lower-alpha;
prefix: "(";
suffix: ") ";
}
ul {
list-style: alpha-modified;
}
Result
Specifications
Specification |
---|
CSS Counter Styles Level 3 # counter-style-system |
Browser compatibility
BCD tables only load in the browser
See also
list-style
,list-style-image
,list-style-position
symbols()
, the functional notation creating anonymous counter styles.