select * from test_regex('?', '', '-');
ERROR: invalid regular expression: quantifier operand invalid
-- These two are not yet incorporated in Tcl, cf
--- https://core.tcl-lang.org/tcl/artifact/106269fa65d96b83
+-- https://core.tcl-lang.org/tcl/tktview?name=5ea71fdcd3291c38
-- expectError 6.21 - {x(\w)(?=(\1))} ESUBREG
select * from test_regex('x(\w)(?=(\1))', '', '-');
ERROR: invalid regular expression: invalid backreference number
select * from test_regex('?', '', '-');
-- These two are not yet incorporated in Tcl, cf
--- https://core.tcl-lang.org/tcl/artifact/106269fa65d96b83
+-- https://core.tcl-lang.org/tcl/tktview?name=5ea71fdcd3291c38
-- expectError 6.21 - {x(\w)(?=(\1))} ESUBREG
select * from test_regex('x(\w)(?=(\1))', '', '-');
-- expectMatch 6.22 HP {x(?=((foo)))} xfoo x