Function parse_reset_region 

pub fn parse_reset_region(
    region: &[OsString],
    wrapper_flags: &[&[u8]],
) -> Result<ResetRegion, OptionError>

What: Parse the region after reset. Result<A, B> is “either success A or failure B”. Why: A region Git itself would refuse yields the refusal; Git then resets nothing.

In TS you’d write (pseudocode):

function parseResetRegion(region: string[], wrapperFlags: string[]): ResetRegion; // throws