What does the use of the final keyword prohibit in PHP?

The keyword final in the context of PHP is used to prevent inheritance and overriding:

1. Finalizing a class: Applying final to a class prohibits creating subclasses that inherit from it.

   <?php
   final class BaseClass {
       // ...
   }
   
   // class DerivedClass extends BaseClass {} // Fatal error: Class DerivedClass cannot inherit from final class BaseClass
   

2. Finalizing a method: Applying final to a method within a class prohibits overriding that method in subclasses.

   <?php
   class ParentClass {
       final public function cannotBeOverridden() {
           // ...
       }
   
       public function canBeOverridden() {
           // ...
       }
   }
   
   class ChildClass extends ParentClass {
       // public function cannotBeOverridden() {} // Fatal error: Cannot override final method ParentClass::cannotBeOverridden()
       public function canBeOverridden() {
           // Overriding is allowed
       }
   }
   

final cannot be applied to class properties.