hp. 25.11.2002 The purpose of this scheme is to define
'smil-related' elements (i.e. 'par' and 'seq' to be used within
neca. This might be replaced by a REAL integration of smil20 one
day.
The 'smil_structure'
group uses this abstract element. Elements with 'struct' as
their substitution class are then alternatives for
'structrure'. Currently these are 'seq' and 'par'
The 'allowed-within-container'
group uses this abstract element. Elements with awc as
their substitution class are then alternatives for
'allowed-within-container'.
These are the 'leafs' allowed in the smil_structure elements
Timing attributes for smil : at the moment
only integer are allowed, which are interpreted as [ms] Later on
values like "3.2s" or "25ms" could be allowed