title: Quotes and inline R code in Rmarkdown YAML
body: <p>I would like to add some special fonts as part of the title/subtitle in an R markdown document but I'm getting different results depending on the quote types I'm using.</p>
  
  <p>Here's a small R markdown example that shows my problem. I would like to print the twitter logo before the twitter handle as part of the R markdown subtitle.</p>
  
  <pre><code>---
  title: "Untitled"
  subtitle: '`r fontawesome::fa("twitter", fill = "steelblue")` @twitter handle'
  author: "My Name"
  date: "7/12/2018"
  output: html_document
  ---
  
  This is it.
  </code></pre>
  
  <p>If I use single quotes then I almost get the result I want. There is a newline between the logo and the twitter handle as shown below but that is fine - it could be fixed with css since the logo is set inside <code>&lt;svg&gt; ... &lt;/svg&gt;</code>. </p>
  
  <p>However, if I use double quotes then things go haywire:</p>
  
  <pre><code>subtitle: "`r fontawesome::fa('twitter', fill = 'steelblue')` @twitter handle"
  </code></pre>
  
  <p>Now <em>none</em> of the YAML information turns up in the final html document. I'm guessing that it is related to <a href="https://stackoverflow.com/questions/23449319/yaml-current-date-in-rmarkdown">this question on entering the current date as part of the yaml</a> or possibly <a href="https://stackoverflow.com/questions/32637340/inline-r-code-in-yaml-for-rmarkdown-doesnt-run">this post where the YAML inline code doesn't run</a> but I am curious as to <em>why</em> the change of quote types in the YAML has such a profound impact on the rendering since the double quotes clearly work for the other YAML parameters.</p>
  
  <p>I'm using <code>rmarkdown</code> v1.10.</p>
  
  <p><a href="https://i.stack.imgur.com/4wraU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/4wraU.png" alt="enter image description here"></a> </p>