Proposed Format

<scoped_address>%<scope_id>

scoped_address: IPv6 scoped address
unicast:  link-locals, site-locals
multicast: all non-globals
should not be used for global addresses, but we didn't prohibit using.
an implementation MAY allow users to use the format for globals

%: delimiter character
seems to have less conflicts than other candidates

scope_id:
decimal number
(optional) implementation dependent notation
MUST uniquely specify a single zone of a scope