title: ggplot right align axis text when using expression
body: <p>I am making a bar chart with long axis labels which i need to wrap and right align. The only complication is i need to add a expression to have superscripts. </p>
  
  <pre><code>library(ggplot2)
  library(scales) 
  df &lt;- data.frame("levs" = c("a long label i want to wrap",
                              "another also long label"),
                   "vals" = c(1,2))
  
  p &lt;- ggplot(df, aes(x = levs, y = vals)) + 
    geom_bar(stat = "identity") +  
    coord_flip() + 
    scale_x_discrete(labels = wrap_format(20))
  </code></pre>
  
  <p>which produces the desired result:  </p>
  
  <p><a href="https://i.stack.imgur.com/lNemk.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/lNemk.png" alt="enter image description here"></a></p>
  
  <p>with properly wrapped text with all labels fully right aligned. </p>
  
  <p>However now I attempt to add superscript using the below code, and the axis text alignment changes: </p>
  
  <pre><code>p &lt;- ggplot(df, aes(x = levs, y = vals)) + 
    geom_bar(stat = "identity") +  
    coord_flip() + 
    scale_x_discrete(labels = c(expression("exponent"^1),
                                wrap_format(20)("another also long label")))
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/wB0ve.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wB0ve.png" alt="enter image description here"></a></p>
  
  <p>(NB I cannot use unicode as is recommended to others with the same question because it does not work with the font I am required to use).</p>
  
  <p>How can I get the axis text to be aligned right even when one of the axis labels includes an expression?   </p>