Function holds_source_in_corner 

pub fn holds_source_in_corner(src: RangeRef, target: RangeRef) -> bool

Whether target is a shape Excel’s AutoFill accepts for src: it contains the source and the source sits in one of its corners. Excel refuses a target that doesn’t contain the source (2:3 into A:A, H4:H9 into D:F) or holds it away from every corner (H4:H9 into H:H).