HTML 5 placeholder in contact.pages.inc

Hi there,

Im totally new to drupal. Iv set up a small site and was wondering if it is possible to add an HTML placeholder with a value to the following code.

$form['mail'] = array(
'#type' => 'textfield',
'#title' => t('Your e-mail address'),
'#maxlength' => 255,
'#default_value' => $user->uid ? $user->mail : '',
'#required' => TRUE,

So you would get something like this I guess.

$form['mail'] = array(
'#type' => 'textfield',
'#title' => t('Your e-mail address'),
'#placeholder' => t('wow it works'),
'#maxlength' => 255,
'#default_value' => $user->uid ? $user->mail : '',
'#required' => TRUE,

This does not work. If any one has got some ideas let me know. Iv been looking on forums for hours and can't find anything about it.

Cheers,
AJCvHall