Regex Character-Class

Greets,

I must be missing something here:

SELECT '1.1.1.1' ~ E'^\d+';

returns FALSE, when I would expect TRUE, as for:

SELECT '1.1.1.1' ~ E'^[[:digit:]]+';

ie, '[[:digit:]]' != '\d'

In config, "regex_flavor = advanced".

Any ideas?

Thanks
Henry