thommy on "Custom Fields in Album"

I'm trying to add custom Fields in Album.
Event_title
Event_parent_id
Event_id

I took the Example from https://github.com/zenphoto/Unsupported/blob/master/plugins/filter-custom_data/filter-custom_data.php


function custom_data_save_album($discard, $prefix) {
return sanitize($_POST[$prefix.'x_album_custom_data'], 1);
}

function custom_data_edit_album($discard, $album, $prefix) {
return
'<tr>
<td align="left" valign="top">'.gettext("Special data:").'</td>
<td><textarea name="'.$prefix.'x_album_custom_data" cols="'.TEXTAREA_COLUMNS.'" rows="6">'.htmlentities($album->get('custom_data'),ENT_COMPAT,getOption("charset")).'</textarea></td>
</tr>';
}

It seems, that's only possible to add one custom field. How is it to realize to use more fields?
Any suggestions? Does somebody has an example?