The ParamModelHandler is a class used to parse XML elements in Logback's configuration files that specify a parameter. Here's an example of how it might be used in a Logback configuration file:

<configuration>
  <param name="param1" value="value1"/>
  <appender name="console" class="ch.qos.logback.core.ConsoleAppender">
    <encoder>
      <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
    </encoder>
  </appender>
  <root level="info">
    <appender-ref ref="console"/>
  </root>
</configuration>

In this example, the element is used to set a parameter called "param1" to the value "value1". This parameter can then be referenced by name in other parts of the configuration, for example as part of a value for another parameter, or as part of a pattern for an appender.

You can add this block in your logback-spring.xml or logback.xml file.

The ParamModelHandler class is responsible for parsing the elements in the configuration file and setting the corresponding values on the LoggerContext object. The ParamModelHandler class is called automatically by the Logback configuration system, you don't need to call it directly.

It's important to keep in mind that this example is just one of the way the ParamModelHandler can be used in Logback configuration. Your specific configuration requirements and the structure of your XML file may vary.