<frequency> CSS数据类型表示频率维度，例如语音的音高。目前它未在任何 CSS 属性中被使用。
<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.
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
0kHz. Though the units are case-insensitive, it is good practice to use a capital "H" for
kHz, as specified in the SI.
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
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>.
|CSS Values and Units Module Level 3
|Candidate Recommendation||Initial definition|
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