Source

File: wp-includes/class-wp-admin-bar.php

final protected function _render_container( $node ) {
		if ( 'container' !== $node->type || empty( $node->children ) ) {
			return;
		}

		echo '<div id="' . esc_attr( 'wp-admin-bar-' . $node->id ) . '" class="ab-group-container">';
		foreach ( $node->children as $group ) {
			$this->_render_group( $group );
		}
		echo '</div>';
	}