code: def flag_single_gifti(img_files):
      """Test if the paired input files are giftis."""
      # Possibly two gifti; if file is not correct, will be caught
      if isinstance(img_files[0], list):
          return False
  
      flag_single_gifti = []  # gifti in pairs
      for img in img_files:
          ext = ".".join(img.split(".")[-2:])
          flag_single_gifti.append(ext == "func.gii")
      return all(flag_single_gifti)
  
label_desc: Use image node_id 1 for calling a global function with example usage: flag_single_gifti(img_files) and returns: all, False