WordPress at a glance
filter is not described

widget_form_callback filter-hook . WP 2.8.0

Filters the widget instance's settings before displaying the control form.

Returning false effectively short-circuits display of the control form.

Usage

add_filter( 'widget_form_callback', 'filter_function_name_4589', 10, 2 );
function filter_function_name_4589( $instance, $this ){
	// filter...

	return $instance;
}
$instance(array)
The current widget instance's settings.
$this(WP_Widget)
The current widget instance.

Where the hook is called

WP_Widget::form_callback()
widget_form_callback
wp-includes/class-wp-widget.php 503
$instance = apply_filters( 'widget_form_callback', $instance, $this );

Where the hook is used (in WP core)

Does not used.