I’m trying to configure a custom appender, and I need to make appender class customisable via properties.

In `ch.qos.logback.core.joran.action.AppenderAction` I see, that `className` is not substituted. It’s strange, cause just a few lines below we use `name` attribute to define appenderName, and we substitute it. 

So, questions are: 

1. Why are we doing it this way?

2. What else can I do, to achieve my goal of having appender class externalised?

Can you help, please?

Context, I’m writing a library, that should do most of logging configurations automatically, and I would like users of the library to be able to extend some behaviour that is only available if we let them have custom appenders.

Cheers, 

Pavel