| start | indicates the location within a temporal alignment
      at which this element begins. | 
|  | Datatype: IDREF | 
|  | Values: contains the identifier of a previously defined <loc> 
element | 
|  | Default: #IMPLIED | 
| Note | If no value is supplied, the element is assumed to follow
   the immediately preceding element at the same hierarchic level. | 
| end | indicates the location within a temporal alignment at which
   this element ends. | 
|  | Datatype: IDREF | 
|  | Values: contains the identifier of a previously defined <loc> 
   element | 
|  | Default: #IMPLIED | 
| Note | If no value is supplied, the element is assumed to
precede the immediately following element at the same hierarchic level.
    | 
| dur | (duration) indicates the length of this element in time, using either
         specific units or the units specified on the associated temporal
         alignment. | 
|  | Datatype: CDATA | 
|  | Values: contains a number optionally followed by a standard unit
         indicator | 
|  | Default: #IMPLIED | 
| Note | If units are not defaulted, they should be represented
         using standard abbreviations (s for second, m for minute, etc.) |