title: is dash a special character in R regex?
body: <p>Despite reading the <a href="http://stat.ethz.ch/R-manual/R-devel/library/base/html/regex.html">help page of R regex</a></p>
  
  <blockquote>
    <p>Finally, to include a literal -, place it first or last (or, for perl
    = TRUE only, precede it by a backslash).</p>
  </blockquote>
  
  <p>I can't understand the difference between</p>
  
  <pre><code>grepl(pattern=paste("^thing1\\-",sep=""),x="thing1-thing2")
  </code></pre>
  
  <p>and </p>
  
  <pre><code>grepl(pattern=paste("^thing1-",sep=""),x="thing1-thing2")
  </code></pre>
  
  <p>Both return TRUE. Should I escape or not here? What is the best practice?</p>