class REXML::Validation::Interleave

def next( event )
  # Find the next series
  next_current(event) unless @events[@current]
  return nil unless @events[@current]
  expand_ref_in( @events, @current ) if @events[@current].class == Ref
  if ( @events[@current].kind_of? State )
    @current += 1
    @events[@current-1].previous = self
    return @events[@current-1].next( event )
  end
  return @previous.pop.next( event ) if @events[@current].nil?
  if ( @events[@current].matches?(event) )
    @current += 1
    if @events[@current].nil?
      return self unless @choices[@choice].nil?
      return @previous.pop
    elsif @events[@current].kind_of? State
      @current += 1
      @events[@current-1].previous = self
      return @events[@current-1]
    else
      return self
    end
  else
    return nil
  end
end