The doc says:

"
[...]

Allows redefining or appending fields to the request header passed to the proxied server. The value can contain text, variables, and their combinations. These directives are inherited from the previous configuration level if and only if there are no proxy_set_header directives defined on the current level. By default, only two fields are redefined: [..]"

Formally the definition is precise. But I suppose I'm not the only one who falls into this trap and thinks that the following configuration piece

server {
proxy_set_header A B;
location / {
proxy_set_header B C;
}
}

will lead to both A and B headers defined, but in reality this leads only to B being defined and A becoming unset. Could the fact that proxy_set_header directive if present on the current level redefines/unsets the whole bulk of headers possibly be accented in the article ?

Thanks.