So I’m a newbie to nginx, and had this same question. Turns out the syntax of the language as mentioned above is both custom and actually quite simple. The syntax is captured in a section in the NGINX docs, and repeated here for convenience:
nginx consists of modules which are controlled by directives
specified in the configuration file. Directives are divided into
simple directives and block directives. A simple directive consists of
the name and parameters separated by spaces and ends with a semicolon
(;). A block directive has the same structure as a simple directive,
but instead of the semicolon it ends with a set of additional
instructions surrounded by braces ({ and }). If a block directive can
have other directives inside braces, it is called a context (examples:
events, http, server, and location).Directives placed in the configuration file outside of any contexts
are considered to be in the main context. The events and http
directives reside in the main context, server in http, and location in
server.The rest of a line after the # sign is considered a comment.
In summary: Everything in an NGINX config file is a directive which may reference a variable. All directives are listed alphabetically here, and all variables are listed alphabetically here. NGINX configuration is driven by modules that each implement a certain piece of functionality, and each module contributes directives and variables that become available for use within the config. That’s it.
That is why even if — which looks like a keyword like in a traditional programming language — is actually just a directive contributed by the ngx_http_rewrite_module module.
Hope this helps!
PS – Also check out https://devdocs.io/, and specifically https://devdocs.io/nginx, for a much improved way to search/use the NGINX documentation.