My understanding is that the double lined tracking box ( [[ ]] ) will track a subject across the entire screen, while the single tracking box ( [ ] ) tracks a subject only within the AF area you are using at the time and anytime [ ] strays outside of the AF area you're using, it will turn from white to gray.
Now, all of this happens without either pressing shutter halfway or pressing back button focus (bbf). So far, I follow Canon's logic.
However, I can't understand the practical difference between [ ] and [[ ]] when actively shooting a moving subject. If I am trying to track a basketball player or an animal, I will already have either my shutter half pressed or the bbf pressed once the tracking box locks onto the subject. This actively tracs the subject across the entire screen (with [ ] OR [[ ]] ), regardless of what AF pattern I was working in. ie once you "lock" tracking on, it doesn't matter if it's a single or a double box doing the work, it will still track across the entire screen AND also continually keeps adjusting focus with the subjects movement in the z direction.
So when actively focusing in Servo then, what is the difference between [ ] and [[ ]] in practical terms? They seem to behave exactly the same.
