A string that matches a Fully Qualified Class Name from PHP, especially not starting with a backslash as this is an invalid character to start a class name with but a somewhat common mistake so this simple type can be used to validate against it already Param name should be unique in scope of type Param name should be unique in scope of virtual type Preference for each class should be unique in scope of file Type name should be unique in scope of file Virtual type name should be unique in scope of file Preference help Object Manager to choose class for corresponding interface With 'type' tag you can point parameters and plugins for certain class With 'virtualType' tag you can point parameters and plugins for autogenerated class