[1] HTMLayout CSS support map http://www.terrainformatica.com/htmlayout/cssmap.whtm#background-position-attribute

expand
Expandable filling mode.
stretch
Image is stretched to fill background in full. This is the same mode as rendering of image in <IMG> element.

(名無しさん [sage])

[2] >>1 例 background-repeat:expand stretch-left stretch-right stretch-middle;

[3] Chrome では inherit など CSS-wide keyword を指定して取得すると inherit inherit のような再度構文解析できない値になります。