Allowed characters in php-fpm pool name

Question

php-fpm allows to configure individual pools.

[poolname]
user = ...
group = ...
listen = 127.0.0.1:9000
...

Which characters are allowed within the square brackets in the first line?

Answer 1

I also could not find the answer anywhere, therefore started experimenting. It turned out that there are no strict limitation on this matter, I was able to run fpm pool with the following names:

[domaincom]
[domain.com]
[*.domain.com]

and even

[Domain: *.domain.com Root: /var/www]

So fpm pool name can be the same as the domain name for convenience, especially while reviewing process tree.