XPath PMD rule to check that Salesforce custom fields contain no underscores

rules.xml

<?xml version="1.0"?>

<ruleset name="Salesforce Custom Rules"
    xmlns="http://pmd.sourceforge.net/ruleset/2.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://pmd.sourceforge.net/ruleset/2.0.0 https://pmd.sourceforge.io/ruleset_2_0_0.xsd">

    <description>
        My Salesforce rules
    </description>


    <rule name="NoUnderscoresInFieldNames"
      language="xml"
      message="Custom fields should not contain underscores."
      class="net.sourceforge.pmd.lang.rule.XPathRule" >
    <description>
TODO
    </description>
    <priority>3</priority>
    <properties>
        <property name="xpath">
            <value>
<![CDATA[
//fields/fullName/text[matches(@Image, ".*_.*__c")]
]]>
            </value>
        </property>
    </properties>
</rule>

</ruleset>