Questions about SPECIAL-USE IMAP extension

I'd like to configure my dovecot service to use the IMAP SPECIAL-USE extension, but have a few questions for those who have used them, or are knowledgable about its use. Using this configuration as an example,

namespace {
	...
	mailbox xxx {
		special_use = \Sent
	}
}

Q1) Am I correct that mail client that don't understand SPECIAL-USE extentions will behave the same way with repect to outgoing mailbox storage?

Q2) Will SPECIAL-USE enabled mail clients switch the mailbox used for outgoing mail from whatever it was using (e.g. "Sent Mail") to the (new) special-use mailbox "xxx"?

Q3) Will SPECIAL-USE enabled mail clients connecting for the first time use "xxx" for outgoing mail, auto-creating it if necessary? Or will "xxx" be used only if the user does not manually configure a mailbox for this purpose?

Q4) If I have an additional configuration

mailbox yyy {
	special_use = \Sent
}

how does it affect Q2, Q3?

Thanks to any who can provide clarity on this.

Joseph Tam <jtam.home@gmail.com>