[firebird-support] substring similar - "Invalid SIMILAR TO pattern"

[liviuslivius liviusliv...@poczta.onet.pl [firebird-support]]

Hi,
 
Firebird 3
 
can someone tell me how to work with substring similar?
 
SELECT substring('abc' similar 'a' escape '#')  FROM RDB$DATABASE
raise an error "Invalid SIMILAR TO pattern"
 
 
SELECT substring('ab11c' similar '[0-9]+' escape '#')  FROM RDB$DATABASE
raise an error "Invalid SIMILAR TO pattern"
 
what i am doing wrong?
how this pattern should looks like?
 
regards,
Karol Bieniaszewski