In most cases, you will find that there is a set method in place that is a wrapper function for set_arg() . In the rare situation where this is not in place, you will need to refer to the GTK source in order to find the argument name expected by this method. There is a short tutorial explaining what to look for, under get_arg() .

The syntax used in this method is as follows:

<?php

$label->set_arg(array('GtkLabel::label'=>'RTFS', 
'GtkLabel::pattern'=>'____'));

?>