Changing Stripe Plans in Cashier?

When you change plans in Cashier with "swap," it seems like it's creating a new Stripe invoice immediately and charging the customer right away, if the new plan is more expensive, and prorating the customer if its a cheaper plan. This is fine, but the documentation does not explain what's happening at all. Is my observation correct? https://laravel.com/docs/5.4/billing#changing-plans

To make matters more confusing, the Stripe documentation says that by default, changing plans in Stripe does not create a new invoice or charge the user right away, but instead prorates the difference and applies it to the upcoming invoice, weather it be more expensive or cheaper. https://stripe.com/docs/subscriptions/upgrading-downgrading

Which is it? What's actually happening in Cashier?