Greasemonkey and <h3>

Hello all

I'm wondering if it is possible for me to read the text in <h3> (there is only 1 <h3>) in the source and input to a text field and submit?

some tips in were to look would be greatful. I have tried a few things with no luck

Cheers

(function() {
var h3 = document.getElementsByTagName('h3')[0];
if ( !!h3 ) {
document.getElementById('some-input').value = h3.innerHTML;
document.getElementById('form-id').submit();
}
})()