Valid characters in nginx configuration

[SW@EU]

Hi,

there can I find the description of the nginx configuration file syntax e.g. in a BNF like notation. There is defined which characters are allowed in "name" e.g. of an upstream definition? Only ASCII or UTF8, only alpha or alphanumeric and if the last, must it start with alpha. Can I use special characters like "@"? IMO is this the basic information which should be on top of the documentation but either is does not exists or is very good stashed ;-)

I'm not the first which ask this in the web: http://stackoverflow.com/questions/36485834/valid-characters-in-nginx-upstream-name, but there is no answer and it is from 10 years ago :-(

Can anyone help me please? Maybe I use wrong search terms.

TIA,
SW

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