Display Border of Box

Hi,

I actually develloping an editor of mathematical formula, and I think that
it's easier for user to see borders of boxes inside function like square
root or also to separate elements in a matrix.
To realize that, I know I have to modify MathMLP.P. But I have made some
modifications  like added "LineWeight:1; ShowBox;" in "SqrtBase" section, I
have compiled this file with Thot Compiler and I haven't seen any box !
Can you help me ?