It is generally recommended to explicitly declare the visibility for methods.
Adding explicit visibility (private, protected, or public) is generally
recommend to communicate to other developers how, and from where this method
is intended to be used.
The PSR-2 coding standard requires that all properties in a class have their visibility explicitly declared. If you declare a property using
the property is implicitly global.
To learn more about the PSR-2, please see the PHP-FIG site on the PSR-2.