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