ee3c8c01_CSS_Masking_Module_Level_1__Computed_value
[Name] mask-position [Value] # [Initial] center [Applies to] All elements. In SVG, it applies to container elements without the element and all graphics elements [Inh.] no [%ages] refer to size of mask painting area minus size of mask image; see text background-position [CSS3BG] [Media] visual [Animatable] as repeatable list of simple list of length, percentage, or calc [Computed value] 
Consisting of: two keywords representing the origin and two offsets from that origin, each given as an absolute length (if given a ), otherwise as a percentage.
CSS Masking Module Level 1
Computed value