Hello Laz,
I understand that 2001:DB8:1234:AB80::/57 is the “optimal” summarization of 2001:DB8:1234:ABA2::/64 and 2001:DB8:1234:ABC3::/64. but I see this summarization include all the pool [2001:0db8:1234:ab80:0000:0000:0000:0000 - 2001:0db8:1234:abff:ffff:ffff:ffff:ffff] …which must be precised in the documentation
then, if there is no constraint in the exibit asking to exclude all before 2001:db8:1234:ab7f:ffff:ffff:ffff:ffff
and all after 2001:0db8:1234:ac00:0000:0000:0000:0000, I think an “industrial” summarization may be 2001:DB8:1234:AB00::/56 (pool from AB00 to ABFF) or, more of that, 2001:DB8:1234:AA00::/55 . then, with a good, industrial (but ip expensive) IP hierarchical organization, no documentation at all must be done.
(I think, for example, about a ccna question asking "is 2001:db8:1234:aa00::/55 a possible summarization of 2001:DB8:1234:ABA2::/64 and 2001:DB8:1234:ABC3::/64)
Am I right ?