Help with code?

[Phil <rhodes@xxxxxxxxxxxxxx>]

    I got the following full moon code from a friend.  I am trying to study
different codes to try to understand them so I can learn more about how to
write code on my own.   I would like someone to explain what each line does
and means in the code below?
    
begin
var:z(0);
If currentbar=1 then begin
z=27303.3;
While z<=datetojulian(date) begin
z=z + 29.531;
end;
end;

if intportion(z)=datetojulian(date) then begin
z=z+ 29.531;
end;

if z-1<datetojulian(date) then z=z+29.531;
if z>z[1] then begin

plot1( high,  "Full Moon");
plot2 (low," Full Moon");

end;

END;
  
  I understand some of the code, but not all!   
 What is 27303.3?  And what does it mean?
 What is does intportion mean?  And why is it used?
 also a simple explaination of datetojulian date?
 I think I understand the rest?  Maybe?

 Any info would be very helpful!!!

                  Thank you,
                  Phil