function valid() does not seem to conform to the naming convention (^(?:is|has|should|may|supports)).
This check examines a number of code elements and verifies that they conform
to the given naming conventions.
You can set conventions for local variables, abstract classes, utility classes, constant, properties,
methods, parameters, interfaces, classes, exceptions and special methods.
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: