Function parse_stash_region 

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

What: Parse the region after stash. Result<A, B> is “either success A or failure B”. Why: Leading wrapper flags are skipped first, so git stash --no-enforce-worktree list still dispatches to list; the rest follows the selected subcommand’s grammar.

In TS you’d write (pseudocode):

function parseStashRegion(region: string[], wrapperFlags: string[]): StashRegion; // throws