Symfony and Eclipse: I can not go to the function or class using F3

I'm using Eclipse (Build id: 20090920-1017) to write my Symfony web application and in many cases I can not "go" to the declaration of functions or classes (you know placing the cursor where the class or the function is called and then pressing F3).

For example: I have this class:

class UsuarioFormFilter extends BaseUsuarioFormFilter{

}

When I try to go to BaseUsuarioFormFilter it doesn't 开发者_如何学Cwork.

How can I make it work?

Your project is configured like php project?

<nature>org.eclipse.php.core.PHPNature</nature>

This works: I just go to the folder that contains BaseUsuarioFormFilter and right click on it and then "Build Path">"Use as source folder".

Nice =) Also, i think you can use "lib" like source folder.