code: def add_heading(self, text="", level=1):
          
          if not 0 <= level <= 9:
              raise ValueError("level must be in range 0-9, got %d" % level)
          style = "Title" if level == 0 else "Heading %d" % level
          return self.add_paragraph(text, style)
docs: Return a heading paragraph newly added to the end of the document.
  
          The heading paragraph will contain *text* and have its paragraph style
          determined by *level*. If *level* is 0, the style is set to `Title`. If *level*
          is 1 (or omitted), `Heading 1` is used. Otherwise the style is set to `Heading
          {level}`. Raises |ValueError| if *level* is outside the range 0-9.