code: def get_revisions(page):
    
    start_string = "    <revision>\n"
    end_string = "    </revision>\n"
    ret = []
    current_pos = 0
    while True:
      start_pos = page.find(start_string, current_pos)
      if start_pos == -1:
        break
      end_pos = page.find(end_string, start_pos)
      assert end_pos != -1
      ret.append(page[start_pos + len(start_string):end_pos])
      current_pos = end_pos + len(end_string)
    return ret
docs: Extract the revisions of a page.
  
    Args:
      page: a string
    Returns:
      a list of strings