Bones0
Smash Legend
This is one of the many things you can use pause to test with. Pause while standing in neutral, hold down+B, then unpause. You will shine because, like Druggedfox said, it's a specific move with an individual input. If you pause, hold Y+Z, then unpause, you will simply jump. The whole idea behind JC grabs is that you go through 1 frame of jumpsquat to use a standing grab instead of a dash grab. Even if grab inputs took priority over jump inputs, you would simply dash grab. However, that's not the case because Melee gives jump inputs priority if you grab or shield on the same frame. I don't remember other priorities, but again, you can test these with pause. Hold Y+A and see which input gets acccepted (jump vs. jab). Sometimes messing up refined tech skill timings can be attributed to this system of input priority.