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.

def add_heading(self, text="", level=1):
        """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.
        """
        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)