At present, the beams of doors are generally strong, and if they are made too much, they will only leave fingerprints at the place where they are made, which is nothing serious.
Whether standards can be formulated depends on the situation. Pull-ups are explained in the manual of "National Physical Training Standards": "After hanging your hands on the bar, bend your arms hard and pull them up until your chin crosses the bar. When pulling the body, you can't use the power of kicking and swinging. " Be sure to cross the bar with your chin.
Mainly because the doorman is uncomfortable. It is the back muscles that are pulled up. If you want to dig by hand, you will practice your fingers:-)