Extending Core Classes in the Application Directory

Certain core concrete5 classes are extendable via classes found in the application/ directory. This extendability happens automatically, if the class is namespaced properly and found in the proper location. Individual component documentation specifies which concrete5 components are extendable in this way, but in general it follows a couple specific rules.

Extending Controllers

If you've ever created your own custom block in the application/ directory, you're somewhat familiar with controller extension. In general, a block type or attribute controllers that's in the core can be extended by creating the same controller in application/.

namespace Application\Block;
class Content extends Concrete\Block\Content\Controller


This same setup works for attribute controllers and core view controllers.

Extending Core src/ Classes

Certain aspects of the core that live in the concrete/src/ are extendable or replaceable with classes in the application directory. For example, let's say you want to extend or replace the concrete5 SecurImage Captcha controller. This controller is located at


This means it has the namespace Concrete\Core\Captcha\SecurimageController.

To use a different controller for this captcha library, simply create one in


And give it the namespace Application\Concrete\Captcha\SecurimageController.

For all items that can be extended in this way, just make sure to add the overriding items to application/src/Concrete, and start the namespace with Application\Concrete.

How do I know which items can be extended in this way?

These should be documented in the Developer Documentation; if you don't see an entry, look in the concrete5 source for the method overrideable_core_class(). It's a hint that the item being instantiated will be loaded from application/ first, before trying the core.

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