title: To replace but the last occurrence of string in a text
body: <p>Suppose I have this piece of text:</p>
  
  <pre><code>Saturday and Sunday and Monday and Tuesday and Wednesday and Thursday and Friday are days of the week.  
  </code></pre>
  
  <p>I want all but the last <code>and</code> to be replaced with a comma:</p>
  
  <pre><code>Saturday, Sunday, Monday, Tuesday, Wednesday, Thursday and Friday are days of the week. 
  </code></pre>
  
  <p>Is there an easy way to do that in regex? As far as I know, the <code>replace</code> method in regex replaces the strings all the way through. </p>