NGINX new features on the help of

NGINX each update will add new features or new variables, I would like
to ask about these new features or new variables, how to use, for
example, to a configuration file reference. For example, the following
variables or parameters

$upstream_cache_status variable.
“updating” parameter
“keepalive_requests” directive
“limit_rate_after” directive.
“proxy_cache_methods” and “fastcgi_cache_methods” directives.
“image_filter_jpeg_quality” directive.

“listen” directive of the mail proxy module supports IPv6.
the ngx_http_image_filter_module.
“try_files” directive
“client_body_in_single_buffer” directive.
“proxy_cache_key” directive.
“fastcgi_cache_key” directive

I hope that every time an official update, not only to write to update
the log, more should be increased use of help or instructions, thanks.