Preparing to upgrade old PostgreSQL and looking changelog, I has found log
about "prefix text match" operator (boosted by SP_GIST):
=> select 'ab' ^@ 'a';
Yes, search on prefix is widely used, indeed. But there is nothing about it
in the documentation. Instead exists only a function "starts_with", may be
this is a different thing. And may be it is not boosted by the index in the
same way, as operator ^@. And functionality is duplicated.