$agent->get('http://genome.ucsc.edu/cgi-bin/hgGateway');
$agent->form_name('mainForm');
$agent->field('clade', 'vertebrate');
$agent->field('org', 'Human');
$agent->field('db', 'hg17');
$agent->field('pix', '620');
$agent->field('position', 'NM_000747');
$agent->click('Submit');