Hi,
We have a tournament registration form set up for multiple players in each team. And we would like one of the input fields to check if the value matches any of the registered users on our site since every contestant should be registered to sign up. Is this possible through the attributes ? If so, could anyone please help me a bit here since I do not know the value that would be placed in there.

Sincerely,
John.

If you simply wish to only allow registered users to submit the form, a much easier solution would be to use the default Joomla! access levels. You can display the form through a menu item and set the access level for that menu item as 'Registered'. This way, only registered users will be able to access the form in order to submit it.

You can also add the following script in Components >> RSForm!Pro >> Manage Forms >> edit your form >> Properties >> PHP Scripts >> 'Scripts called on form display' area:

JHTML::_('behavior.tooltip');
$user = JFactory::getUser();
if($user->id <= 0)
$formLayout = 'Log in first';

This script will only allow the displaying of the form's layout if the user accessing it is logged in.