title: How to get `mtext()` with partial bold text?
body: <p>I would like to add a text to my plot so that one letter, <strong>a</strong>, appears bold. I started with the following, but the result is not what I need:</p>
  
  <pre><code>plot(1:5,axes=F)
  mtext(c(only a should be bold),1:1,font=2)
  </code></pre>
  
  <p>What should I do to make only a bold?</p>