Bootstrap 3 panel shortcode

used for this tutorial
https://generatewp.com/?p=11889

// Add Shortcode
function shortcode_handler( $atts , $content = null ) {

	// Attributes
	extract( shortcode_atts(
		array(
			'header' => 'no',
			'footer' => 'no',
			'type' => 'default',
		), $atts )
	);

	// Code
	//make sure the panel type is a valid styled type if not revert to default
	$panel_types = array('primary','success','info','warning','danger','default');
	$type = in_array($type, $panel_types)? $type: 'default';

	//start panel markup
	$output = '<div class="panel panel-'.$type.'">';

	//check if pannel has a header
	if ('no' != $header)
		$output .= '<div class="panel-heading">'.$header.'</div>';

	//add panel body content and allow shortcode in it
	$output .= '<div class="panel-body">'.trim(do_shortcode( $content )).'</div>';

	//check if pannel has a footer
	if ('no' != $footer)
		$output .= '<div class="panel-footer">'.$footer.'</div>';

	//add closing div tag
	$output .= '</div>';

	//return shortcode output
	return $output;
}
add_shortcode( 'bs3_panel', 'shortcode_handler' );