An SMU is unlikely to be the correct granularity for all hypermedia applications, or even for all extent specifications in a single application. For example, HMUs with such values as 24 and 30 per second can be used for synchronization with motion pictures and video. It must have been declared as the notation name of a data content notation with a formal public identifier that is a measurement unit. Multiple measurement domain definitions with the same domain SMU are treated as defining a single measurement domain. This rule makes it easy to supplement a standard measurement domain definition with granules needed for a specific document.
Granule names are case-sensitive.
A granule name cannot be the same as another granule name in the same measurement domain. A granule name cannot be the same as the SMU name of its measurement domain. As granule names are case-sensitive and SMU names are not, case is ignored when applying this rule. Multiple measurement domain definitions for the same SMU comprise one domain. The ratio is specified as a pair of numbers, the first being the numerator and the second being the denominator.