id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	uname	nginx_version
2414	support unknown variables when it is only used in log format	gentle-king@…		"currently, when we add some extend variable in log format which is not yet defined with ""set"" or other command, it will raise emerg error: unknown ""xxxxxx"" variable. so if you want change log field, depend on other config, server block, eg.

sometimes it is needed to extend variables in logs in batch, and the variable, is set only in some instance, and is not set in other instance.

it can be as $http_ or $arg_, even $http_xxxx variable is not found in head, it will not raising error when writing log, and not raise error when do test or reload. 
for every variable, of only used in log format, just not raise error. or for specify variables, add similar way: $ngx_ext_ , eg.
"	enhancement	closed	minor		nginx-module	1.21.x	wontfix			Linux cent82-2c4g 4.18.0-348.7.1.el8_5.x86_64 #1 SMP Wed Dec 22 13:25:12 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux	"nginx version: nginx/1.21.4
built by gcc 8.5.0 20210514 (Red Hat 8.5.0-4) (GCC) 
built with OpenSSL 1.1.1o  3 May 2022
TLS SNI support enabled
configure arguments: --prefix=/home/ngx/nginx --with-http_ssl_module --with-http_v2_module --with-http_realip_module --with-http_sub_module --with-http_mp4_module --with-http_gunzip_module --with-http_gzip_static_module --with-http_auth_request_module --with-http_addition_module --with-openssl=/home/ngx/build_ngx/openssl-1.1.1o --with-zlib=/home/ngx/build_ngx/zlib-1.2.11 --with-pcre=/home/ngx/build_ngx/pcre-8.45"