Class used for data exchange with the payment system. It contains an enterprise of classes. The principles of class functioning depend on the chosen mode of operation.

Every class created by means of Engine can be easily broaden. Only constructor of the class and class $_arrayField requires modification. It is desirable to make the names of the keys in the array $_arrayField identical, but this is not obligatory.

The places in the body of the class used for class modification are underlined by the following comment: \*** MODIFIED CODE ***\. Also the folder 'systems' contains file tmpl_system.php which stands for the template for the class of the payment system.