Comment by recursive
In the 90s, we used Server Side Includes (SSI) for this. Probably still works.
In the 90s, we used Server Side Includes (SSI) for this. Probably still works.
httpd, nginx, a number of other servers support SSI
https://nginx.org/en/docs/http/ngx_http_ssi_module.html
Caddy chose not to, I guess?
https://caddy.community/t/caddy-update-on-ssi-server-side-in...
However, you could generate the static HTML easily and then publish it on those platforms, which is what many people do today (probably not often using SSI).
One modern approach would be Caddy Server's templates, using Golang templating:
https://caddyserver.com/docs/modules/http.handlers.templates
The "include" function should do the job:
{{include "path/to/file.html"}}