rsyslog Lookup Tables Missing Manual

Since a very long time, the rsyslog documentation mentions a lookup table feature, but as a proposal only. However, it is fully implemented as of version 8.18.0 and should become official “very soon”.

On top of this, there is a bug in the documentation so the page explaining the actual implementation is not linked from anywhere. You can find it here, and hopefully some search engines will pick it up soon as well.