Extension folder Classes for PHP classes 
            
    Contains all PHP classes. One class per file. Should have sub folders like
Controller/, Domain/, Service/ or View/.
For more details on class file namings and PHP namespaces, see chapter
namespaces.
Typical PHP classes in this folder:
Classes/Controller/SomeController.php
- 
            
- Scope
 - extension
 - Path (Composer)
 - packages/my_extension/Classes/Controller/SomeController.php
 - Path (Classic)
 - typo3conf/ext/my_extension/Classes/Controller/SomeController.php
 
Contains MVC Controller classes. In Extbase extensions the classes inherit from
\TYPO3\.CMS\ Extbase\ Mvc\ Controller\ Action Controller See also chapter Extbase Controller.
 
Classes/Domain/Model/Something.php
- 
            
- Scope
 - extension
 - Path (Composer)
 - packages/my_extension/Classes/Domain/Model/Something.php
 - Path (Classic)
 - typo3conf/ext/my_extension/Classes/Domain/Model/Something.php
 
Contains MVC Domain model classes. In Extbase they inherit from
\TYPO3\. See also Extbase Model.CMS\ Extbase\ Domain Object\ Abstract Entity  
Classes/Domain/Repository/SomethingRepository.php
- 
            
- Scope
 - extension
 - Path (Composer)
 - packages/my_extension/Classes/Domain/Repository/SomethingRepository.php
 - Path (Classic)
 - typo3conf/ext/my_extension/Classes/Domain/Repository/SomethingRepository.php
 
Contains data repository classes. In Extbase a repository inherits from
\TYPO3\. See also Extbase Repository.CMS\ Extbase\ Persistence\ Repository  
Classes/ViewHelpers/MyViewHelper.php
- 
            
- Scope
 - extension
 - Path (Composer)
 - packages/my_extension/Classes/ViewHelpers/MyViewHelper.php
 - Path (Classic)
 - typo3conf/ext/my_extension/Classes/ViewHelpers/MyViewHelper.php
 
Helper classes used in Fluid templates. See also Developing a custom ViewHelper.