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.
In PHP it is possible to write to properties without declaring them. For example, the following is perfectly valid PHP code:
Generally, it is a good practice to explictly declare properties to avoid accidental typos and provide IDE auto-completion: