nginx FAQ [Is there a proper way to use nginx variables to make sections of the configuration shorter, using them as macros for making parts of configuration work as templates?](https://nginx.org/en/docs/faq/variables_in_config.html) ) saying (bold is mine):

> 
> Q: Is there a proper way to use nginx variables to make sections of the configuration shorter, using them as macros for making parts of configuration work as templates?
> 
> 
> A: Variables should not be used as template macros. **Variables are evaluated in the run-time during the processing of each request, so they are rather costly compared to plain static configuration**. Using variables to store static strings is also a bad idea. Instead, a macro expansion and "include" directives should be used to generate configs more easily and it can be done with the external tools, e.g. sed + make or any other common template mechanism.
> 
> 
> 

For example instead of one super long `add_header Content-Security-Policy` for better readability I am using:

```
set $CSP "default-src 'none'";

set $CSP "${CSP}; connect-src 'self'";

set $CSP "${CSP}; script-src 'self' https://*.domain.org 'unsafe-inline' 'unsafe-eval'";

set $CSP "${CSP}; style-src 'self' https://*.domain.org 'unsafe-inline'";

set $CSP "${CSP}; img-src 'self' data: https://*.domain.org";

set $CSP "${CSP}; font-src 'self' https://*.domain.org";

## CSP closing colon.
set $CSP "${CSP};";

add_header Content-Security-Policy "$CSP";

```

How much impact on nginx performance would that use of variable have appropriately? Has there been any performance testing / research on that subject?