title: How to show more rows in selectMultiple widget?
body: <p>How might one tell <a href="http://ipywidgets.readthedocs.io/en/latest/examples/Widget%20List.html#SelectMultiple" rel="nofollow noreferrer">the selectMultiple widget</a> to show more rows?</p>
  
  <pre><code>widgets.SelectMultiple(
      options=GROUP_NAMES,
      description='Groups',
      disabled=False,
  )
  </code></pre>
  
  <p>The html equivalent of adding <a href="https://www.w3schools.com/tags/att_select_size.asp" rel="nofollow noreferrer">a size attribute</a> <code>size=10</code> to the select tag.</p>
  
  <p>Not this but that...</p>
  
  <p><a href="https://i.stack.imgur.com/a4yeF.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/a4yeF.png" alt="defaults to 3 rows"></a></p>
  
  <p><a href="https://i.stack.imgur.com/jm96G.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/jm96G.png" alt="but we want lots of rows"></a></p>