2008-12-13 17:09:53: Description changed to 'SMIL has elaborate rules for computing time spans, however in order to simplify timed text processing some constraints are imposed by dfxp which can lead to unexpected results if no time attributes are specified.
A seq element is defined to have a simple duration of indefinite, rather than based on the active duration of its children, thus at last one of dur or end should be defined on a seq to limit its simple duration.
Should we add a validity constraint to require:
a) require either dur or end on seq
b) prevent using both dur and end on the same element?
' [Sean Hayes]