docs: def process_documentline(line, nanopubs_metadata):
      """Process SET DOCUMENT line in BEL script"""
  
      matches = re.match('SET DOCUMENT\s+(\w+)\s+=\s+"?(.*?)"?$', line)
      key = matches.group(1)
      val = matches.group(2)
      nanopubs_metadata[key] = val
  
      return nanopubs_metadata