I have a code for read all inputs in a form.
The code works in my demo page an others, but not work in some pages. For the example issue:
facebook:
$url = 'https://www.facebook.com';
$html = file_get_html($url);
$post = $html->find('form[id=reg]'); //id for the register facebook page
print_r($post);
Print an empty array.
Functional example:
$url = 'http://www.monografias.com/usuario/registro';
$html = file_get_html($url);
$post = $html->find('form[name=myform]');
print_r($post);
Print a form content
Facebook won't give you registration form directly, it will only respond with basic html, and the rest will be created with javascript. see for yourself
$url = 'https://www.facebook.com';
$html = file_get_html($url);
echo htmlspecialchars($html);
there is no form with "reg" ID in the html they send you.