code: def concat_ast(asts: Sequence[DocumentNode]) -> DocumentNode:
      
      return DocumentNode(
          definitions=list(chain.from_iterable(document.definitions for document in asts))
      )
docs: Concat ASTs.
  
      Provided a collection of ASTs, presumably each from different files, concatenate
      the ASTs together into batched AST, useful for validating many GraphQL source files
      which together represent one conceptual application.