There's been a lot of chatter about a recent RFC from Pádraic Brady on the php.internals maling list - his proposal to add native escaping to the PHP core. He shares some of his own thoughts about the proposal in a new post to his site.
A short time ago today, I submitted a PHP RFC for discussion which proposes adding an SPL Escaper class and, quite possibly, a related set of functions dedicated to escaping data for output to HTML/XML to PHP: https://wiki.php.net/rfc/escaper. The RFC itself should be a good read if you want to understand why I'm proposing this but the basics are quite simple. Cross-Site Scripting (XSS) is one of the two most common security vulnerabilities in web applications - the other being SQL Injection. Despite this, PHP's offering of escaping functions is extremely limited.
He talks about what problems the proposed solution solves and how it could help protect PHP programmers more effectively than the more complicated methods they have to go through now. If you're interested in reading the conversations so far, you can start here and walk through the messages.