[PD] pd and tk

[Alex from Idoia]

Hello,
This is a newbie question about how pd works with tk on OSX:
in the directory bin of pd, there is a file called pd.tk and I suppose 
the code inside is used when we use the menu bar in pd and for dealing 
with all the new windows etc... what is this language ? Actually when I 
open pd, the main window is somewhere in between the middle and the 
left of the screen, so I thought I could change its position on the 
screen to fit my needs. I think I found the line code :
canvas .dummy -height 2p -width 9c
I tried several time to add randomly some options like -xpos or xscreen 
but nothing worked....
Generally, tk is used for MAC no ? but what is its first purpose and 
how where can find info to how to modify its code ? finally what is tcl 
then ?
Thanks.