def _rect(x: float,
          y: float,
          boxwidth: float,
          boxheight: float,
          fill: str = 'white',
          strokewidth: float = 1):
    """Draw an SVG <rect> rectangle."""
    return f'<rect x="{x}" y="{y}" width="{boxwidth}" height="{boxheight}" ' \
           f'stroke="black" fill="{fill}" stroke-width="{strokewidth}" />'