if i enable the cache plugin with coredns:1.10.1 like this:

services.example.net {
   cache 60 . {
     success 524288
     denial 524288
    keepttl
 }
}

I get:

plugin/cache: Corefile:94 - Error during parsing: Wrong argument count or unexpected line ending after 'keepttl'

If i remove keepttl or the . zone from the config the server starts normally:

services.example.net {
   cache 60 {
     success 524288
     denial 524288
     keepttl
   }
}

For me it is not directly clear why this is the case from the documentation, so i think this is a bug in the config parser log, or something is missing in the documentation