{
          "title" => "The Dream of %{author}'s %{pet}",
          "author" => "%{authorFirst} %{authorLast}",
		  "authorFirst" => "Jim",
          "authorLast"  => "Bo",
          "pet"    => "cat"
}

Passing the above function in, the first run through would yield:

{
          "title" => "The Dream of %{author}'s %{pet}",
          "author" => "Jim Bo",
		  "authorFirst" => "Jim",
          "authorLast"  => "Bo",
          "pet"    => "cat"
}

which would call itself again since there still exists %{} values, the next run through would yield:

{
          "title" => "The Dream of Jim Bo's cat",
          "author" => "Jim Bo",
		  "authorFirst" => "Jim",
          "authorLast"  => "Bo",
          "pet"    => "cat"
}