Check for keyframe on another layer

[cwellems]

I have two layers, A and B. LayerA is a precomp containing drawings for an animation, with time remapping keyframes to display the drawings in the correct locations on the timeline. LayerB is a precomp containing a sequence of 5 texture images. I'd like to write an expression on LayerB to change the frame it is displaying whenever a keyframe is present in LayerA.

I found the following expression on this forum which works well, although I'd like to understand better what var t is. I know it is used to break the for loop but that's about it.

seedRandom(1,true);
var t=timeToFrames();
var r1=-3;
var r2=-2;
var r3=-1;
for (var i=0;t>=i; i++) {
   var r3=Math.floor(random(5));
   if (r1==r3 || r2==r3) {
      t++;
      continue;
   }
   r1=r2;
   r2=r3;
}
framesToTime(r3);

As for checking for the presence of a time remap keyframe on another layer, I'm clueless as to where to start. Any advice would be appreciated.

[Mylenium]

Not sure what you need to know. Isn't it obvious what a verbose functiuon called timeToFrames() does? It's literally spelled out.

Mylenium