Documentation of advanced settings in search sets

I was wondering what does activating Search Sets -> Advanced -> Search in: “Keywords”, “Description”, and “Objects” do?

The documentation only says “Choose which parts of a document DEVONagent Pro searches for the query. Not all file types have all characteristics.”

These are HTML entities, e.g.,…

  <meta charset="UTF-8">
  <meta name="description" content="Really Important Stuff">
  <meta name="keywords" content="Money,Love,Madness">
  <meta name="author" content="Some Smart Guy">