code: def convert(document):
      
      raw_tokens = []
      curpos = 0
      text_spans = []
      all_labels = []
      sent_spans = []
      word_texts = []
      for sentence in document:
          startpos = curpos
          for idx, (text, label) in enumerate(sentence):
              raw_tokens.append(text)
              word_texts.append(text)
              all_labels.append(label)
              text_spans.append((curpos, curpos+len(text)))
              curpos += len(text)
              if idx < len(sentence) - 1:
                  raw_tokens.append(' ')
                  curpos += 1
          sent_spans.append((startpos, curpos))
          raw_tokens.append('\n')
          curpos += 1
      return {
          TEXT: ''.join(raw_tokens),
          WORDS: [{TEXT: text, START: start, END: end, LABEL: label} for text, (start, end), label in zip(word_texts, text_spans, all_labels)],
          SENTENCES: [{START: start, END:end} for start, end in sent_spans]
      }
docs: Convert a document to a Text object