'natural' (default): natural-language / "find documents about this text" search.
'boolean': operator-aware search (dialect-specific boolean/text-search
operator syntax, e.g. MySQL boolean-mode +word -word "phrase", MSSQL
CONTAINS, Oracle Text CONTAINS operators).
'phrase': exact-phrase search where the dialect has a distinct,
better-suited construct for it (e.g. Postgres websearch_to_tsquery,
MySQL boolean-mode quoted phrase, MSSQL/SQLite quoted phrase).
Search mode for
fullTextMatch().+word -word "phrase", MSSQLCONTAINS, Oracle TextCONTAINSoperators).websearch_to_tsquery, MySQL boolean-mode quoted phrase, MSSQL/SQLite quoted phrase).