code: public function getSkylineAppDirectory(string $dirName) {
          $name = CC::get([], $dirName);
          if($name) {
              return $this->getSkylineAppDataDirectory() . "/$name";
          }
          return NULL;
      }
docs: Returns the required Skyline CMS Application data sub directory
  
  @param string $dirName
  @return string
  @see CompilerConfiguration::SKYLINE_DIR_* constants