undary 
    of a variable-width X-spline.
  </p>
    <p>
    In the <a href="#offset-curves">Offset curves</a> Section, 
    we establish a general definition
    of offset curves and the <a href="#x-spline-curves">X-spline curves</a> Section
    describes the equations for X-spline curves.  The
    <a href="#x-spline-tangent">X-spline tangent functions</a> Section generates expressions for
    the tangent to an X-spline curve and the
    <a href="#rendering">Rendering X-spline offset curves</a> Section des