Here is an example of a class extending SiftModelHandler in Logback:

import ch.qos.logback.core.sift.SiftModelHandler;
import ch.qos.logback.core.sift.SiftingAppender;

public class MySiftModelHandler<E> extends SiftModelHandler<E> {
    private SiftingAppender<E> siftingAppender;

    public MySiftModelHandler(SiftingAppender<E> siftingAppender) {
        this.siftingAppender = siftingAppender;
    }

    @Override
    public void start() {
        // additional initialization code
        super.start();
    }

    @Override
    public void handle(E event) {
        // handle logic
        super.handle(event);
    }
}

This class is an example of a custom Sift Model Handler in Logback, which is used to handle events that are passed to the SiftingAppender. It extends SiftModelHandler, a class that provides a way to handle events which are passed to the SiftingAppender. The SiftingAppender is passed in the constructor and is used to handle the events.

The start method is overridden to perform additional initialization. The handle method is overridden to define the logic for handling the events. The handle method is called by the SiftingAppender for each event that is passed to it, and it is responsible for determining which appender should handle the event based on the discriminator value.

It is important to note that this class is extending SiftModelHandler which is a base class for handling events which are passed to the SiftingAppender. The SiftingAppender class separates logging events based on a discriminator value, and the handle method is responsible for determining which appender should handle the event based on the discriminator value.