[firebird-support] Why this similar to is wrong?

[sirhamac...@gmail.com [firebird-support]]

select 
        iif('em...@testdomain.com' similar to 
'([_a-zA-Z\d\-\.]+@[_a-zA-Z\d\-]+(\.[_a-zA-Z\d\-]+)+)','ok','fail')
 
 from rdb$database
 

 Says 'invalid string' and 'invalid pattern', but the pattern it´s the same in 
other languages for validate email address.