title: RMarkdown error in YAML
body: <p>I watched a great webinar by RStudio the other day about RMarkdown.  After the webinar they posted the code used in the demonstrations online and I wanted to check out one example. I took <a href="https://raw.githubusercontent.com/rstudio/webinars/master/2014-01/4-linked-brush.Rmd">their code</a>, put it in my RStudio (which says it's fully up-to-date, v0.98.978), installed or updated all the necessary packages and hit "Run Document"</p>
  
  <p>I receive an error which I do not understand and for which Google has been very unhelpful.   What is this mysterious &lt;document start&gt; and how do I include it?  I assumed all necessary components would be included given the source of the code.</p>
  
  <pre><code>Error in yaml::yaml.load(front_matter) : 
    Parser error: did not find expected &lt;document start&gt; at line 2, column 1
  Calls: &lt;Anonymous&gt; -&gt; parse_yaml_front_matter -&gt; &lt;Anonymous&gt; -&gt; .Call
  Execution halted
  </code></pre>