# Namespaces and Class Names of User Files¶

The namespace and class names of user files follow the same rules as class names of the TYPO3 Core files do.

The namespace declaration of each user file should show where the file belongs inside its extension. The namespace starts with "Vendor\MyNamespace\", where “Vendor” is your vendor name and “MyNamespace” is the extension name in UpperCamelCase. Then follows the name of the subfolder of Classes/, in which the file is located (if any). E.g. the file typo3conf/ext/realurl/Classes/Controller/AliasesController.php with the class AliasesController is in the namespace “DmitryDulepov\Realurl\Controller”.

User files with these class names are commonly found in the typo3conf/ext/ directory. Optionally these files can be installed to the typo3/ext/ directory to be shared by many TYPO3 installations.