title: <unescaped bksl>S4method Error when documenting a replacement function
body: <p>I want to document a replacement function in R, but when I run R CMD check I get this error message:</p>
  
  <pre><code>Bad \usage lines found in documentation object 'timestamps':
    &lt;unescaped bksl&gt;S4method{"timestamps&lt;-"}{.MoveTrack}(this, value)
  
  Functions with \usage entries need to have the appropriate \alias
  entries, and all their arguments documented.
  The \usage entries must correspond to syntactically valid R code.
  </code></pre>
  
  <p>the documentation looks like this:</p>
  
  <pre><code>\name{timestamps}
  
  \alias{timestamps}
  \alias{timestamps,.MoveTrack-method}
  \alias{timestamps,.MoveTrackSingle-method}
  \alias{"timestamps&lt;-",.MoveTrack-method}
  
  \docType{methods}
  
  \title{Extract the timestamps of a Move or MoveStack object}
  
  \description{The timestmaps method returns or sets the timestamps of a track from a Move or MovesStack object.}
  
  \usage{
  \S4method{timestamps}{.MoveTrackSingle}(this)
  \S4method{timestamps}{.MoveTrack}(this)
  \S4method{"timestamps&lt;-"}{.MoveTrack}(this, value)
  }
  
  \arguments{
    \item{this}{Move or MoveStack object}
    \item{value}{timestamps from class POSIXct}
  }
  </code></pre>
  
  <p>and the actual function is the following:</p>
  
  <pre><code>setGeneric("timestamps", function(this) standardGeneric("timestamps"))
  setMethod("timestamps", ".MoveTrack",
     function(this) {
        this@timestamps
     })
  
  setMethod("timestamps", ".MoveTrackSingle",
            function(this) {
              this@timestamps
            })
  
  setGeneric("timestamps&lt;-", function(this, value) standardGeneric("timestamps&lt;-"))
  setReplaceMethod("timestamps", ".MoveTrack",
     function(this, value) {
        this@timestamps &lt;- value
        this
     })
  </code></pre>
  
  <p>I searched for the error message but all I found was about Roxygen documentation which didn't help me. I also tried different documentation styles like :</p>
  
  <pre><code>\S4method{"timestamps&lt;-"}{.MoveTrack}(this, value)
  \S4method{"timestamps&lt;-."}{.MoveTrack}(this, value)
  \S4method{"timestamps&lt;-$"}{.MoveTrack}(this, value)
  \S4method{'timestamps&lt;-'}{.MoveTrack}(this, value)
  \S4method{timestamps&lt;-}{.MoveTrack}(this, value)
  \S4method{"timestamps\&lt;\-"}{.MoveTrack}(this, value)
  \S4method{"timestamps\\&lt;\\-"}{.MoveTrack}(this, value)
  </code></pre>
  
  <p>but non of them worked. Any idea?
  Thanks a lot in advance. 
  best, marco</p>