Documentation of a program is done by another program called the Parser which is the part of a program’s compiler that goes through a program line by line looking for all predefined characters allowing it to recognize calls to a pre-defined function in it’s library files (Similar to C’s LIB files where functions were pre-defined and called from) these pre-defined functions can be accessed by including the include file in the initialization phase of compilation where the parser recognizes the call, gets the definition of the function, uses it with the provided information and returns to the program for the next operation. This is more of the very fundamental workings of programming languages and how compilers understood the code which was written in a text editor. You will appreciate this later on when applications become more and more complex and debugging sends you tugging on your hair for hours on end to find the problem and fix it.