PHP programming forum. Ask questions or help people concerning PHP code. Don't understand a function? Need help implementing a class? Don't understand a class? Here is where to ask. Remember to do your homework!
I believe subforms are part of the Drupal Content Management System as I am pretty sure they are not part of standard HTML. As such I cannot really comment in detail. You may want to look at the specific documentation. My only suggestion in regards to PHP if you have results needing processing is that you output the $_GET or $_POST result arrays and see what the form(s) actually return.