In a new post to the Exakat blog they propose an interesting idea: making everything private in your PHP classes with the basic idea being that you can more easily move from a place with more control (private) to less control (protected/public).
It is a good recommendation to make everything private in a class : constants, methods, properties. With private, comes a tighter control on the element : no one from outside may use it, limiting the unwanted impact on the object. Of course, some of the class has to be accessible from the outside, or the object may only be manipulated as a token.
[...] Eventually, when the code matures, it becomes desirable to apply the above principle of encapsulation. This helps keeps the code clean and made of independent components. This is the beginning of a long hunt.
They show how the results look for an Exakat scan of a class and go through each of the results touching on class constants, methods and properties. It also catches when a class property is a "constant" and not modified - or able to be modified - by any means. The post ends with a recommendation to "update your code with your brain" based on the interpretation of the results.