function parse($value, &$pipeline)
 {
     $style = new ListStyleValue();
     $style->image = CSSListStyleImage::parse($value, $pipeline);
     $style->position = CSSListStylePosition::parse($value);
     $style->type = CSSListStyleType::parse($value);
     return $style;
 }
 function is_default()
 {
     return $this->image->is_default() && $this->position == CSSListStylePosition::default_value() && $this->type == CSSListStyleType::default_value();
 }