This has been implemented off the quick search tips which are found here on the php.net 'Tips and Tricks' page :
Also, if you haven't yet implemented the quick search feature into your browser(s), you should (instructions found at php.net/tips.php). It allows one to quickly search the manual in an intelligent and useful manner, sound good? Read about it at the above link and you won't be sorry. Not only does it allow for intelligent searching straight from your browsers command line but this means less typing too.
In summary, explained are two forms of intelligent php manual searching. Good luck and remember: The Manual Is Your Friend.