Image scaling behaviors.
This type can have following values:
"none"- The image is not scaled.
"fill"- Scale each dimension to exactly fit destination, the aspect ratio of the image is no preserved.
"down"- If it is too large for the destination, scale the image down while preserving the aspect ratio.
"up-or-down"- Scale the image to its maximum possible dimensions while both staying within the destination area and preserving its aspect ratio.