code: def prepare(self):
          
          result_files = self.collect_files()
          chain = self.prepare_handlers_chain
          if chain is None:
              # default handlers
              chain = [
                  LessCompilerPrepareHandler()
              ]
          for prepare_handler in chain:
              result_files = prepare_handler.prepare(result_files, self)
          return result_files
docs: Called when builder run collect files in builder group
  
          :rtype: list[static_bundle.files.StaticFileResult]