magento-test/dev/tests/integration/testsuite/Magento/Config/_files/system.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Config:etc/system_file.xsd">
    <system>
        <section id="general">
            <group id="group">
                <group id="subgroup">
                    <field id="field" translate="label" type="text" sortOrder="100" showInDefault="1" showInWebsite="1" showInStore="0">
                        <label>Label</label>
                    </field>
                    <field id="second_field" translate="label" type="text" sortOrder="10" showInDefault="1" showInWebsite="1" showInStore="0">
                        <label>Label Second</label>
                        <config_path>custom/config_path/second_field</config_path>
                    </field>
                </group>
            </group>
        </section>
    </system>
</config>