[ipv6-wg] is use of IF-ID 0 "clean"

Dear WG-folks, out of curiosity and because I got asked this question, here we go: Is the use of "0" as the interface ID in an IPv6 network "clean"? I haven't found any indication that "0" is reserved (as in IPv4), or should not be used, but there's a lingering feeling that it may cause trouble, somewhere, somehow. Any input appreciated, tia, Wilfried.