A TTML time expression.
This template takes a time expression as used by the begin, end, and dur attributes and returns the number of seconds that expression respresents. Time expressions may be any number parsable by the XPath number function followed by one of the units ms (milliseconds), s (seconds), m (minutes), or h (hours). It returns 0 if the time expression is invalid.
This template provides support only for the #time-offset TTML feature. It does not support other methods of specifying times.