// count number of plots in layer and set all to be hidden
layer.color=color(white);//need to have a color to clear background with plot -l
nplots=0;
doc -e D {set %C -s 0;nplots++};

set %(1,@D) -s 1;// show 1st plot
plot -l; // draw layer

loop (i,2,nplots) {
  sec -p 1;
  set %(i-1,@D) -s 0;
  set %(i,@D) -s 1;
  plot -v; // disable flash
  plot -l;
};