[Templates] Nonexistent variables in templates

[Filin]

Hi.

When I use in template a "nonexistent" variable, I just get an undefined value.
Is it possible to change this somehow?

If I want something tricky with certain variable, I can pass to the template a sub or an object instead of plain scalar/hash/array. That sub could, for example, throw an exception - thus  I can
effectively disable some variables (names), or log them, check them, etc.
But what if I want something tricky with ALL used in template variables?