<configuration>

  <conversionRule conversionWord="sample"
    converterClass="ch.qos.logback.classic.testUtil.SampleConverter" />

  <appender name="LIST" class="ch.qos.logback.core.testUtil.StringListAppender">
    <layout class="ch.qos.logback.classic.html.HTMLLayout">
      <Pattern>%sample%msg</Pattern>
    </layout>
  </appender>

  <root level="debug">
    <appender-ref ref="LIST" />
  </root>
</configuration>