code: def extract_ids(text, extractors):
      
      for extractor in extractors:
          for id in extractor.extract(text):
              yield id
docs: Uses `extractors` to extract citation identifiers from a text.
  
      :Parameters:
          text : str
              The text to process
          extractors : `list`(`extractor`)
              A list of extractors to apply to the text
  
      :Returns:
          `iterable` -- a generator of extracted identifiers