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\, 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
EXT:
with the class Aliases is in the namespace
"\Dmitry".
User files with these class names are commonly found in the directory vendor/.