public function columns($xs, $sm, $md, $lg)
    {
        $framework = $this->getFramework();
        switch ($framework)
        {
            case 'bs3':
            case 'bs4':
                $xsC = $this->cssClass('column_extra_small') . $xs;
                $smC = $this->cssClass('column_small') . $sm;
                $mdC = $this->cssClass('column_medium') . $md;
                $lgC = $this->cssClass('column_large') . $lg;
                return $this->buildClassString([$xsC, $smC, $mdC, $lgC]);
            case 'f6':
                // Build the foundation classes
                $smC = $this->cssClass('column_small') . $sm;
                $mdC = $this->cssClass('column_medium') . $md;
                $lgC = $this->cssClass('column_large') . $lg;
                $columns = $this->cssClass('column');
                // Build the string
                return $this->buildClassString([$columns, $smC, $mdC, $lgC]);
            default:
                return '';
                break;
        }
    }