On the PHP 10.0 Blog, there's a new post today talking about variable tainting and what it might be like if PHP included it too.

Perl and Ruby have variable tainting. Maybe PHP should have it too?

Variable tainting is a bit of built-in functionality that provides a "safety net" of sorts to the contents of variables to help protect both the users and the script itself from potentially harmful content.

He talks about how Ruby and Perl handle the functionality and how, were PHP to work it in, which approach would fit better with PHP's current model:

If one wants to implement proper tainting or sandboxing, it probably should be based on more generic approach that would account for existence of functions unknown in design time.