When defining custom counter styles, the negative descriptor lets the author alter the representations of negative counter values, by providing a way to specify symbols to be appended or prepended to the counter representation when the value is negative. If the counter value is negative, the symbol provided as value for the descriptor will be prepended to the counter representation; and a second symbol if specified, will be appended to the representation. The negative descriptor has effect only if the system value is symbolic, alphabetic, numeric, additive, or extends, if the extended counter style itself uses a negative sign. If the negative descriptor is specified for other systems that don't support negative counter values, then the descriptor is ignored.
The speak-as descriptor specifies how a counter symbol constructed with a given @counter-style will be represented in the spoken form. For example, an author can specify a counter symbol to be either spoken as its numerical value or just represent it with an audio cue.
The additive-symbols descriptor is similar to the symbols descriptor and allows the user to specify symbols to be used for counter representations when the value of the system descriptor is additive. The additive-symbols descriptor defines what are known as additive tuples, each of which is a pair containing a symbol and a non-negative integer weight. The additive system is used to construct sign-value numbering systems such as the Roman numerals.
The fallback descriptor can be used to specify a counter style to fall back to if the current counter style cannot create a marker representation for a particular counter value. If the specified fallback style is also unable to construct a representation, then its fallback style will be used. If a valid fallback style is not specified, it defaults to decimal. A few scenarios where fallback style will be used are:
The pad descriptor can be used with custom counter style definitions when you need the marker representations to have a minimum length. If a marker representation is smaller than the specified pad length, then the marker will be padded with the specified pad symbol. Marker representations longer than the pad length are constructed as normal. Pad descriptor takes the minimum marker length as an integer and a symbol to be used for padding as the second parameter. A common usage of the pad descriptor is when you need your list to start numbering from 01 and go through 02, 03 and so on, instead of just 1, 2, 3...
The prefix descriptor of the @counter-style rule allows authors to specify a symbol that will be prepended to the marker representation. If no value is specified, the default value will be the empty string.
When defining custom counter styles, the range descriptor lets the author specify a range of counter values over which the style is applied. If a counter value is outside the specified range, then the fallback style will be used to construct the representation of that marker. Value of the range descriptor can be either auto or a comma separated list of lower and upper bounds specified as integers.
The suffix is used with @counter-style to specify a symbol that will be appended to the marker representation. A symbol can be a string, image or a CSS identifier. If not specified, the descriptor assumes the default value "\2E\20" ("." full stop followed by a space).
The symbols descriptor is used to specify the symbols that the specified counter system will use to construct counter representations. A symbol can be a string, image, or identifier. The symbols descriptor must be specified when the value of the system descriptor is cyclic, numeric, alphabetic, symbolic, or fixed. When the additive system is used, the additive-symbols descriptor is used to specify the symbols.
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.