How to get the changes in the layout before doing save through SKILL code?

Hi,

I have scenario, where i want to know what changes happened to the virtuoso layout window before saving, So, i can apply my check code if that change containing my layer.

 Please let me know if we have any built-in functions which can get the stack stored in undo-redo as it store the changes before save.

Thank you,

mallikarjunpm