What is the logic of the transfusional compatibility concerning the ABO blood group system?

A transfusional compatibility for the ABO system takes into account the antigens present in the red blood cells of the donor and the antibodies that the recipient can produce. When the recipient isn't able to produce antibodies against antigens of the red blood cells of the donor the transfusion is compatible. So regarding ABO compatibility type A can donate to type A and to type AB. The Type B can donate to type B and to type AB and the Type AB can donate only to type AB. Type O can donate to all ABO types (Blood transfusion must be studied, planned and supervised by doctors.)