title: Line plus shaded region for error band in matplotlib's legend
body: <p>I would like to have a legend similar to 
  <a href="https://i.stack.imgur.com/TyRRj.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/TyRRj.png" alt="graph with uncertainty band"></a> </p>
  
  <p>but with the dashed line and the yellow region merged like this:</p>
  
  <p><a href="https://i.stack.imgur.com/hQ5uu.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/hQ5uu.png" alt="enter image description here"></a></p>