[kps]

‘whence’ is POSIX-reserved even in shells that don't implement it¹. (‘what’ is also in POSIX². And ‘who’ is on first³.)

¹ https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V...

² https://pubs.opengroup.org/onlinepubs/9699919799/idx/utiliti...

³ https://youtu.be/kTcRRaXV-fg