4.1 Demonstrate ability to write code using core and Object Oriented PHP
Review the differences between an abstract class and a base class. Review PHP constants.
A base class creates consistent reusable code. When you extend a class the new subclass inherits all methods from the parent class.
An abstract class provides a template for inheriting base class methods. Abstract classes cannot be instantiated
An interface provides methods but does not define how to use the methods.
PHP constants are global variables and must always be declared in
UPPERCASE according to Drupal coding standards.