What is the technique of 'Trail Braking' and how is it properly used by advanced riders?

1. Dragging the rear brake continuously while traveling on straight highways
2. Carrying light front brake pressure past the corner entry and gradually tapering off braking pressure as the motorcycle lean angle increases toward the apex
3. Locking both wheels with the parking brake while riding through deep sand
4. Applying full emergency braking only after exiting a corner onto a straightaway