e k/2 nearest points with lower x values are
  included in the window.  When <code>method="nobs"</code>, k equals
  <code>width</code> (actually 2*floor(<code>width</code>/2) ).  When
  <code>method="fraction"</code>, <code>width</code> specifies what fraction of the
  total number of points should be included. The actual number of points
  included in each window will be floor(n*frac/2)*2.  Regardless of the
  value of <code>pts</code>, the function <code>fun</code> will be evaluated at all
  x locations.<