Example of how to customize the ShortVariable rule in PHP Mess Detector

custom_naming.xml

<?xml version="1.0" encoding="UTF-8"?>
<ruleset name="Custom Naming Rules"
         xmlns="http://pmd.sf.net/ruleset/1.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://pmd.sf.net/ruleset/1.0.0 http://pmd.sf.net/ruleset_xml_schema.xsd"
         xsi:noNamespaceSchemaLocation="http://pmd.sf.net/ruleset_xml_schema.xsd">
    <description>
Customizations for the naming rule sets. Do not include the naming ruleset in the options.
This customization pulls all naming rules in and overrides some properties.
    </description>

    <rule ref="rulesets/naming.xml">
        <!-- To be able to customize a property on the ShortVariable rule it must first be excluded.
        Does not really make sense, but see https://github.com/phpmd/phpmd/issues/33 for details. -->
        <exclude name="ShortVariable"/>
    </rule>

    <rule ref="rulesets/naming.xml/ShortVariable">
        <properties>
            <!-- Add common variable names that should be excepted from the default minimum property value of 3 -->
            <property name="exceptions" description="Comma-separated list of exceptions" value="id"/>
        </properties>
    </rule>

</ruleset>