Min/max width with percentage

Love the min/max width/height feature.
Let’s kick it to the upper level of the awesomeness!
I’m wondering if it would be possible to set the width and height (and by extension min/max) in percentage (so it would take the % of the width/height of the direct parent container. That would be huuuge!
You will probably just have to figure out how to deal with % when the object has no container.