I recommend starting with the regex(7) man page, before comparing 
any implementation to another.

> But, iirc vis regex are different from Guile's
> I might be wrong on that.

‘By default, Guile supports POSIX extended regular expressions.’ — 
(guile)Regexp Functions

‘[vis] uses what POSIX refers to as “Extended Regular 
Expressions”’ — vis(1)

Kind regards,

T G-R