Remember that containers are widgets that can contain other widgets. The
simplest type of container is GtkBin - it can only hold one child widget. An
example of this container is a regular button.
To add to or remove a widget from such a container:
<?php
$container->add($widget);
$container->remove($widget);
?>
To obtain all the widgets in a container, use one of the following approaches.
<?php
$child_widgets = $container->children();
$child_widgets = $container->children;
?>
In either case $child_widgets will be an array of immediate children, but
the second approach lets you access a specific child directly, e.g.
$container->children[0].
