The AppenderWithinAppenderSanityChecker class from the logback.core package can be used to check for nested appenders within appenders in a Logback configuration.

Here is an example of how the AppenderWithinAppenderSanityChecker class could be used to check for nested appenders in a Logback configuration:

import ch.qos.logback.core.Context;
import ch.qos.logback.core.joran.spi.JoranException;
import ch.qos.logback.core.joran.spi.InterpretationContext;
import ch.qos.logback.core.status.StatusChecker;
import ch.qos.logback.core.util.AppenderWithinAppenderSanityChecker;

// ...

Context context = new LoggerContext();
InterpretationContext interpretationContext = new InterpretationContext(context, new SubstituteComponentRuleAction());

StatusChecker checker = new StatusChecker(context);
AppenderWithinAppenderSanityChecker sanityChecker = new AppenderWithinAppenderSanityChecker(checker);

try {
    // ... configure interpretationContext with appenders ...
    sanityChecker.checkForNestedAppenders(interpretationContext);
} catch (JoranException e) {
    // handle exception
}

if (checker.isErrorFree()) {
    // configuration is error-free
} else {
    // there were errors in the configuration
}

In this example, an InterpretationContext object is created and configured with appenders, and then passed to the checkForNestedAppenders() method of the AppenderWithinAppenderSanityChecker class. This method will check for nested appenders within appenders in the configuration and will raise an exception if any are found. The context and interpretationContext objects are created and configured with appenders and passed to the checkForNestedAppenders() method.

This class is mainly used to check for nested appenders within appenders. It's not necessary to use this class as part of a Logback configuration, but it can be useful for detecting errors or unintended configurations.

A StatusChecker object is used to check the status of the configuration after the sanity check has been performed. If there are no errors in the configuration, the isErrorFree() method of the checker will return true and the configuration can be used. If there are errors, the isErrorFree() method will return false and the errors will be reported in the logback status.