public function getSpanClassNames(DBViewports $span = null)
    {
        $classes = [];
        
        if (!$span) {
            $span = $this->owner->getSpanViewports();
        }
        
        if ($span->allEqualTo('auto')) {
            
            // Add Span Prefix Only:
            
            $classes[] = $this->spanPrefix;
            
        } elseif ($span->allEmpty()) {
            
            // Add Column Span Defaults:
            
            foreach ($this->columnSpanDefaults as $viewport => $value) {
                $classes[] = $this->getSpanClass($viewport, $value);
            }
            
        } else {
            
            // Add Column Span Field Values:
            
            foreach ($span->getViewports() as $viewport) {
                $classes[] = $this->getSpanClass($viewport, $span->getField($viewport));
            }
            
        }
        
        return $classes;
    }