docs: def folder(self) -> typing.Union[str, None]:
          """
          The folder, relative to the project source_directory, where the file
          resides
  
          :return:
          """
  
          if 'folder' in self.data:
              return self.data.get('folder')
          elif self.project_folder:
              if callable(self.project_folder):
                  return self.project_folder()
              else:
                  return self.project_folder
          return None