Set a layer to 100% opacity.
Let's say you've got an animating layer with changing opacity. You want to
alter the animation but can't always see it because it's fading in and out.
To temporarily ignore the keyframed opacity values, just add this expression
to the layer's opacity:
When you want to use the keyframes again, just turn the expression off by
clicking the = button beside Opacity.
NOTE: The last line of any expression is what gets converted into the value
for that property.
The only property an expression has any control over is the one it's applied
to. This is the reason you don't need to say:
opacity = 100
The "opacity =" bit is automatically assumed anyway.