NOT a regex expert!
@mmotti uses in his regex list
^(www[0-9]*\.)?xn--
which translates into:
your regex
(\.|^)xn--.*\..*$
translates into
whith the example from here, using 'xn--c1yn36f'
mmotti regex101 result: match, 8 steps
your result: NO match
I wonder which one is more efficient and recommended?
couldn't match, because(\.|^)xn--.*\..*$ says that there must be at least a single dot behind xn–c1yn36f.
To have a regex closer to a FQDN without specifying the domain exactly i prefer(\.|^)xn--.*\..+$
Then a dot and at least one letter is needed like xn–c1yn36f.c
and so on....
I'm very new to regex too, but meanwhile i love it. It's great what you can do with it.
Why are you guys looking to specify a regexp for the FQDN incl tlds? You only need a partial match for it to block and it could be adding extra steps / processing where not necessary
Right,
It could!
While learning about Regex I tested all my filter "creations" to see what I'm doing there and how I could get the best results even with an eye on processing and clarity. I found that these points are often and unexpectedly compromising. Sometimes a more precise specification is helpful in saving processing power, and sometimes it is not. If not I prefer precision.
That's cool 
Just as a warning, this is the reason my regex isn't open to all subdomains: Google play issues
Just in case you guys happen to encounter similar problems. I never nailed down the exact cause (e.g. If only affecting users outside of the UK etc), but I had to tweak it for my list due to the number of people it could have potentially caused issues for.
