Hi Anju,
This is actually part of ABAP coding, which is also being supported by Dynamic Actions (as you may know, dynamic actions are actually ABAP code which can be interpreted.
The command "P0367-AECD0+15(1)='X'" means that the system will place the value 'X' in the 15th position of P0367-AECD0 field.
The number in brackets define how many characters of the value will be used, e.g., if we would have written "P0367-AECD0+15(2)='XYZ'", then on the 15th position the system will write the characters XY.
Regards,
Liran