src/test/resources/com/puppycrawl/tools/checkstyle/configurationloader/InputConfigurationLoaderCustomMessages.xml

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE module PUBLIC
    "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
    "http://checkstyle.sourceforge.net/dtds/configuration_1_3.dtd">

<module name="Checker">
    <property name="tabWidth" value="4" />
    <property name="basedir" value="${checkstyle.basedir}" />
    <module name="TreeWalker">
        <module name="MemberName">
            <property name="format" value="^m[a-zA-Z0-9]*$"/>
            <message key="name.invalidPattern"
                     value="Member ''{0}'' must start with a lowercase ''m'' (checked pattern ''{1}'')."
                     />
        </module>
    </module>
</module>