3.5. CSS2 Units
In addition to what we've covered, CSS2 adds a small number of new units, almost all of which are concerned with aural style sheets (employed by those browsers that are capable of speech). We'll briefly cover them here:
- Angle values
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Used to define the position from which a given sound should seem to originate. There are three type of angles: degrees (deg ), grads (grad ), and radians (rad ). For example, a right angle could be declared as 90deg, 100grad , or 1.57rad ; in each case, the values are translated into degrees in the range through 360. This is also true of negative values, which are allowed. The measure -90deg is the same as 270deg.
- Time values
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Used to specify delays between speaking elements, these values can be expressed as either milliseconds (ms) or seconds (s). Thus, 100ms and 0.1s are equivalent. Time values may not be negative.
- Frequency values
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Used to declare a given frequency for the sounds that speaking browsers can produce. Frequency values can be expressed as hertz (Hz) or megahertz (mHz) and cannot be negative. The values labels are case-insensitive, so 10mHz and 10mhz are equivalent.
In addition to these values, there is also an old friend with a new name. A URI is a Uniform Resource Identifier, which is sort of another name for a Uniform Resource Locator (URL). The difference is, for now, mostly semantic, but many authors are beginning to adopt the convention of referring to online addresses as URIs, not URLs. The specification still requires that URIs be declared with the form url(...), though, so it's hard to know exactly what the point was of including a section in CSS2 about how CSS2 uses URIs instead of URLs.
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| 3.4. URLs |  | 3.6. Summary |
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