what does map do?

[paul jobs]

   1. function(doc) {
   2.   if (doc.doctype == "WikiPage") {
   3.     map([doc.title, doc.revision], doc);
   4.   }
   5. }
   *
   *
   *this doesnt output any rows, is there any purpose as to this view*
   *
   *
   *reference: http://prematureoptimization.org/blog/archives/59*