Who can help explain the forehand and backhand of film shooting?

Definition of "positive and negative". This should be a rule of arranging combination shots on the shooting scene, and 90% of them are used in scenes of two-person dialogue (in fact, the scene shooting of multi-person dialogue can still form a fait accompli by cutting the space of the lens). The characteristic of shooting is that A and B look at each other or stand opposite each other or sit opposite each other. The camera is generally fixed in three positions, with the front half or close-up of B behind A, the front half or close-up of A behind B, and the small panorama on AB side. The general framing is "over the shoulder", that is, shooting the front of the speaker's opponent over the shoulder of the person with his back to the camera. According to the key points of the script dialogue, you can switch to insert several shoulder-less close-ups as a supplement to the forehand and backhand combination. Forehand and backhand also have different forms of variation. For example, in a dialogue scene shot in a car, two people sit side by side, but the camera position basically crosses one person's position to shoot another person's chest or face when talking, which forms a fait accompli of forehand and backhand, and so on.

According to the particularity of positive and negative shooting, I don't know who made a set of rather rigid conventions called "axis" principle, that is, draw an imaginary axis vertically through the plane opposite to AB, and the three positions taken by the camera must be on one side of the axis, otherwise it will be accused of "jumping the axis". There will be a fairly comprehensive and detailed criticism of this rule and why there is a corresponding concept.