code: function elmPartiallyObscured(elm, bgElm, bgColor) {
  	var obscured =
  		elm !== bgElm && !dom.visuallyContains(elm, bgElm) && bgColor.alpha !== 0;
  	if (obscured) {
  		axe.commons.color.incompleteData.set('bgColor', 'elmPartiallyObscured');
  	}
  	return obscured;
  }
docs: Determine if element is partially overlapped, triggering a Can't Tell result
  @private
  @param {Element} elm
  @param {Element} bgElm
  @param {Object} bgColor
  @return {Boolean}