title: Use of @ in R programming, or R markdown?
body: <p>I've downloaded code from another programmer, and they have the following:</p>
  
  <pre><code>#' @param gr                a GRanges of regions/DMRs/whatever
  #' @param HMM               a GRanges with ChromHMM annotations (name, itemRgb)
  #' @param background        a null distribution (universe) whence gr was chosen
  #' @param footprint         compute BP footprints instead of number of overlaps?
  #' 
  #' @return                  a data.frame with overlap frequency and color code
  #'
  #' @export
  </code></pre>
  
  <p>I recognize the #' as syntax from knitr spin.  But I don't understand how it's being used here or what the <code>@</code> symbol is doing.  Please explain.</p>