The <frequency> CSS data type represents a frequency dimension, such as the pitch of a speaking voice. It is not currently used in any CSS properties.
Syntax
The <frequency> data type consists of a <number> followed by one of the units listed below. As with all CSS dimensions, there is no space between the unit literal and the number.
Units
Hz-
Represents a frequency in hertz. Examples:
0Hz,1500Hz,10000Hz. kHz-
Represents a frequency in kilohertz. Examples:
0kHz,1.5kHz,10kHz.
Note: Although the number 0 is always the same regardless of unit, the unit may not be omitted. In other words, 0 is invalid and does not represent 0Hz or 0kHz. Though the units are case-insensitive, it is good practice to use a capital "H" for Hz and kHz, as specified in the SI.
Examples
Valid frequency values:
12Hz Positive integer 4.3Hz Non-integer 14KhZ The unit is case-insensitive, though non-SI capitalization is not recommended. +0Hz Zero, with a leading + and a unit -0kHz Zero, with a leading - and a unit
Invalid frequency values:
12.0 This is a <number>, not an <frequency>, because it is missing a unit. 7 Hz No space is allowed between the number and the unit. 0 Although unitless zero is an allowable <length>, it's an invalid <frequency>.