1 Comparison operation for tsquery
2 Btree index on tsquery
3 numnode(tsquery) - returns 'length' of tsquery
4 tsquery @ tsquery, tsquery ~ tsquery - contains, contained for tsquery.
  Note: They don't gurantee exact result, only MAY BE, so it
  useful only for speed up rewrite functions
5 GiST index support for @,~
6 rewrite():
        select rewrite(orig, what, to);
        select rewrite(ARRAY[orig, what, to]) from tsquery_table;
        select rewrite(orig, 'select what, to from tsquery_table;');
7 significantly improve cover algorithm