Method push

src/navigate.rs:148–151

(&mut self, position: NavigationPosition, command: &'static str)

    fn push(&mut self, position: NavigationPosition, command: &'static str) {
        self.position_stack.push(position);
        self.command_stack.push(command);
    }

    fn pop(&mut self) -> Option<(NavigationPosition, &'static str)> {
        assert_eq!(self.position_stack.len(), self.command_stack.len());