Headers explanation

[ejgutierrez74]

Nice tutorial but would be nice to explain the different headers in different files_ like:

header("Access-Control-Allow-Origin: *");
header("Content-Type: application/json; charset=UTF-8");
header("Access-Control-Allow-Methods: POST");
header("Access-Control-Max-Age: 3600");
header("Access-Control-Allow-Headers: Content-Type, Access-Control-Allow-Headers, Authorization, X-Requested-With");

Why are there ? Are there optional or mandatory ? because the files have different header ? For exmple read.php has only two headers...

Would be nice also to have a non-object oriented version of this tutorial.....