Function validate 

pub fn validate(input: &ComputerWait) -> Result<(), String>

Input validation for computer_wait: an element target (selector + exactly one app scope), a 1-based nth, and a timeout within the cap.

Errors

Returns Err for a missing/blank selector, name and pid together, no app scope at all, a 0-based nth, or a timeout_ms above MAX_WAIT_MS.