title: What's the difference between is and inherits?
body: <p>If I want to check whether a variable inherits from some class, I can either use <a href="http://www.inside-r.org/r-doc/methods/is" rel="noreferrer"><code>is</code></a> or <a href="http://www.inside-r.org/r-doc/base/inherits" rel="noreferrer"><code>inherits</code></a>.</p>
  
  <pre><code>class(letters)
  ## [1] "character"
  is(letters, "character")
  ## [1] TRUE
  inherits(letters, "character")
  ## [1] TRUE
  </code></pre>
  
  <p>Is there a preference for which one I should use, and do they ever return different values?</p>