docs: def simple_preprocess(doc, deacc=False, min_len=2, max_len=15):
      """
      Convert a document into a list of tokens.
  
      This lowercases, tokenizes, de-accents (optional). -- the output are final
      tokens = unicode strings, that won't be processed any further.
  
      """
      tokens = [
          token for token in tokenize(doc, lower=True, deacc=deacc, errors='ignore')
          if min_len <= len(token) <= max_len and not token.startswith('_')
      ]
      return tokens