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HTML

<?
/**
 * Plugin Name: New Plugin
 * Description: Widget plugin
 * License: GPL2
 */

$glblplgnme = 'New Plugin';

function mynewplugin() {
	register_widget( 'mynewplugin' );
}
add_action( 'widgets_init', 'mynewplugin' );

class mynewplugin extends WP_Widget {

	function mynewplugin() {
		// Instantiate the parent object
		global $glblplgnme;
		parent::__construct( false, $glblplgnme );
	}

	function widget( $args, $instance ) {
		// Widget output
			extract( $args );
			$title = apply_filters('widget_title', $instance['title']);
			echo $before_widget;
			if ( $title ) { echo $before_title . $title . $after_title; }
		?>

<?
echo 'outout';
?>
		
		<?
			echo $after_widget;
}

	function update( $new_instance, $old_instance ) {
		// Save widget options
						 $instance = $old_instance;
			  // Fields
			$instance['title'] = strip_tags($new_instance['title']);
			$instance['advadtype'] = $new_instance['advadtype'];
			$instance['advcode'] = $new_instance['advcode'];
			$instance['advbnrurl'] = $new_instance['advbnrurl'];
			$instance['advbnrimg'] = $new_instance['advbnrimg'];
			$instance['advbnrtxt'] = $new_instance['advbnrtxt'];
			$instance['advadssnum'] = $new_instance['advadssnum'];
			$instance['advpostnum'] = $new_instance['advpostnum'];
			$instance['flwnflw'] = $new_instance['flwnflw'];
			 return $instance;
	}

	function form( $instance ) {
		// Output admin widget options form
				// Check values
					if( $instance) {
						 $title = esc_attr($instance['title']);
					} else {
						 $title = '';
					}
					?>

					<script type="text/javascript">
jQuery(document).ready(function(){
    jQuery('#kopko').change(function() {
        jQuery("#" + this.value).show().siblings().hide();
    });
    jQuery("#kopko").change();
});			
</script>

<select id="kopko">
<option value="box1">Box 1111</option>
<option value="box2">Box 2222</option>
<option value="box3">Box 3333</option>
</select>

<div>
<div id="box1"><p>Box 1 stuff...</p></div>
<div id="box2"><p>Box 2...