title: Knitr re double hash marks in output
body: <p>I am reading <a href="https://rads.stackoverflow.com/amzn/click/com/B00DJE0C9I" rel="nofollow noreferrer" rel="nofollow noreferrer">"Reproducible research with R and RStudio"</a>. On page 29 the author writes that, using `knitr' this code:</p>
  
  <pre><code>Number &lt;- 10
  Number
  </code></pre>
  
  <p>should yield</p>
  
  <pre><code>## [1] 10
  </code></pre>
  
  <p>In the footnote he says that <code>knitr</code> automatically adds the double hashmarks.</p>
  
  <p>Yet when I type:</p>
  
  <pre><code>library(knitr)
  number &lt;- 10
  number
  </code></pre>
  
  <p>I get</p>
  
  <pre><code>[1] 10
  </code></pre>
  
  <p>just as if I had not installed <code>knitr</code>.</p>
  
  <p>This is minor, but it might be important later in the book.</p>