The <frequency> CSS data type represents a frequency dimension. The format of a time value is a <number> followed by a case-insensitive unit of frequency: Hertz or kilohertz.
Notes and Trivia
CSS <length> values allow removing the unit identifier from a value when that value is zero. When a <frequency> value is zero, on the other hand, the unit can not be omitted, as 0 alone won’t be a valid <frequency> value without its unit.
Hertz is a family noun, and so even though the units are case-insensitive and can be written in all-uppercase, all-lowercase, or capitalized forms, it is recommended to keep the H in uppercase at all times, and not to capitalize the other letters, thus abiding to the grammatical rules of the International System of Units.
Values
- Hz
- Hertz. It represents the number of occurrences per second.
- kHz
- KiloHertz. A kiloHertz is 1000 Hertz.
Examples
The following are all valid frequency values:
0kHz
75Hz
200KHZ /* valid, though not recommended */
-30000Hz
The following are invalid frequency values:
-10 Hz /* no space is allowed between the number and the unit */
0 /* 0 must have a unit of frequency */
5900 /* must have a unit of frequency */
Browser Support
The frequency value is not supported by any browser at this time.
Notes
The <frequency> data type is used in CSS properties that apply to a media type aural, which was introduced in CSS 2. The type aural is now deprecated, but the <frequency> data type has been reintroduced in CSS Level 3 in the Speech module defined for speech output, and which is a re-work of the previous CSS2 aural media group. The CSS properties defined in the Speech module enable authors to declaratively control the presentation of a document in the aural dimension, and the <frequency> values are used in properties that control the voice pitch.