Chapter 12 (full-text search) quietly changed under this book in Postgres 18: FTS now reads its dictionaries and config through the cluster's default collation provider instead of always libc, so clusters on ICU or the new builtin PG_UNICODE_FAST can see different behavior in FTS and pg_trgm — the release notes explicitly tell you to reindex those indexes after pg_upgrade. Also in 18, LIKE with nondeterministic collations stopped being an error, which was the main reason people avoided case-insensitive ICU collations on searchable columns.