Tobias Schlitt has a great (long) post responding to a proposal made on the php.internals mailing list for the inclusion of "taint mode" in upcoming PHP versions.
Tobias starts with an overview of what "taint mode" is so that everyone's on the same page. His example involves the incoming and outgoing data usually involved in an application and how the incoming can be the most problematic when it comes to the values inside. This is where taint mode can come to the rescue. At its most basic level, it's a method for, assuming everything coming in is "tainted", creating a mechanism to automatically clean the data before it's even touched.
With the basics down, Tobias looks back to the proposal for a few additional comments. He considers the proposal a great way to introduce the functionality to the language. There are some draw backs he mentions, though, including the additional overhead of working through every inputted value.
Overall, I think this whole thing would be a great addition to PHP and I hope this could come for 6.0. What do you think?
You can also check out some other opinions on the matter: