The list of options is the same list of form without use php:
http://www.w3schools.com/tags/tag_form.asp
The difference is that the attributes will be passed in array format:
array('action' => 'user.update', 'enctype' => 'multipart/form-data', 'method' => 'PUT')
The default method is POST, if not especified.
@edit
Seems that i didn't let clear.
Laravel only include some atributes to help, how url(converted to action), route(converted to action), file(converted to enctype='multipart/form-data'), but yet same thing.
file to enctype conversion:
if (isset($options['files']) && $options['files'])
{
$options['enctype'] = 'multipart/form-data';
}