title: Is there a way to word wrap or insert a line break with Altair labels?
body: <p>Is there a way to insert a line break when displaying longer labels in Altair?</p>
  
  <pre><code>d = {'source': ['short label', 'a longer label that needs a line break', 'short label', 'a longer label that needs a line break'], 'variable': ['begin','begin','end','end'], 'value':[75, 25, 20, 80]}
  df = pd.DataFrame(data=d)
  
  slope = alt.Chart(df).mark_line().encode(x='variable:N',y=alt.Y('value:Q',scale=alt.Scale(domain=(0,100))),color='source')
  text = slope.mark_text(align='left',baseline='middle').encode(text='source:N')
  (slope + text).properties(width=200)`
  </code></pre>
  
  <p>I see a <a href="https://stackoverflow.com/questions/57116167/how-can-i-put-a-line-break-in-a-vega-lite-axis-title">list of arrays in an option</a> for a title but I haven't been able to get that to work for labels.</p>