title: What does "not run" mean in R help pages?
body: <p>Sometimes on an R help page the phrase "not run" appears in comments. Check out this from the help page for "with()":</p>
  
  <pre><code>Examples
  require(stats); require(graphics)
  #examples from glm:
  **## Not run:** 
  library(MASS)
  with(anorexia, {
      anorex.1 &lt;- glm(Postwt ~ Prewt + Treat + offset(Prewt),
                      family = gaussian)
      summary(anorex.1)
  })
  ## End(**Not run**)
  </code></pre>
  
  <p>What does the "not run" mean in the example code?</p>