title: What is the difference between <pubDate> and <lastBuildDate> in RSS?
body: <p>I have the feeling, in every RSS.xml file, both the pubDate and the lastBuildDate match.</p>
  
  <p>I am sure that this one, is not always true... </p>
  
  <p>So firstly, what is the difference between those two above?</p>
  
  <p>Secondly, the RSS readers, sort the content by Date, based on the pubDate or the lastBuildDate?</p>