The explanations of the par, seq and excl elements seem informative.
Please make them so, and add a normative statement saying that these
elements are defined in the SMIL 3.0 Timing and Synchronization module.
"The excl element defines a time container with semantics based upon
par,but with the additional constraint that only one child element may
play at any given time."
It's not clear to the SVG WG whether this is a constraint added by
Timesheets or by SMIL Timing and Synchronization.
"If any element begins playing while another is already playing, the
element that was playing is stopped."
Please clarify what it means that "playing is stopped". Is the timeline
paused, reset, or something else? What happens if the time first
animation is started again?
What happens if an animation is running in one "slide", and the user
navigates away, then returns? What state is the animation in?