It's also possible to hide a slot (for example when an user is not authorized to see a content or a functionality). To do this is enough to set $_obweb->showslot=false in the slot PHP script. It is strongly advised to return from the slot function after this otherwise the rest of the script would be executed anyway.

<?php
function core_test_()
{
    global $_obweb;

    if (some condition) {
        $_obweb->showslot=false;
        return;
    }
}
?>