Using clip markers to drive layer opacity

Question

Hi folks, I need a little help with an expression. Your input would be most appreciated.
I'd like to have a solid layer in my comp which has 0% opacity most of the time, but has 100% opacity only on those frames where there is a clip marker on a specified footage layer, AND the frames where the footage layer has a clip marker on an adjacent frame.
That last part may be confusing, but the practical upshot is that the layer is transparent until a clip marker comes along, whereupon it goes opaque for the surrounding three frames.
Thanks again!
Ari

Answer 1

// expression 1
L = thisComp.layer("footage");
if (L.marker.numKeys > 0){
if (Math.abs(L.marker.nearestKey(time).time - time) <= thisComp.frameDuration*1.1){
100
}else{
0
}else{
0
// expression 2
L = thisComp.layer("footage");
n = 0;
if (L.marker.numKeys > 0){
n = L.marker.nearestKey(time).index;
if (L.marker.key(n).time > time + thisComp.frameDuration*1.1){
n--;
n
Dan