Chapter 13 showed modifyMeta() as a direct but error-prone way to change field configuration. For the most common case - showing/hiding a field based on another field's value - there's a cleaner, purely declarative mechanism: imports/exports.

Practical case: company field only for "business customer"

Suppose the testimonial form gets a new boolean field is_business_customer - the company field should only be visible when that checkbox is checked. Purely declaratively via switcherConfig:

<field name="is_business_customer" formElement="checkbox">
    <settings>
        <valueMap>
            <map name="false" xsi:type="number">0</map>
            <map name="true" xsi:type="number">1</map>
        </valueMap>
        <dataType>boolean</dataType>
        <label translate="true">Business Customer</label>
    </settings>
    <formElements>
        <checkbox>
            <settings>
                <switcherConfig>
                    <rules>
                        <rule name="0">
                            <value>0</value>
                            <actions>
                                <action name="0">
                                    <target>mironsoft_testimonial_form.mironsoft_testimonial_form.general.company</target>
                                    <callback>hide</callback>
                                </action>
                            </actions>
                        </rule>
                        <rule name="1">
                            <value>1</value>
                            <actions>
                                <action name="0">
                                    <target>mironsoft_testimonial_form.mironsoft_testimonial_form.general.company</target>
                                    <callback>show</callback>
                                </action>
                            </actions>
                        </rule>
                    </rules>
                    <enabled>true</enabled>
                </switcherConfig>
            </settings>
        </checkbox>
    </formElements>
</field>

switcherConfig reacts directly in the browser to value changes, with no server round trip at all - the target path again matches the full namespace chain from form.xml (namespace.provider.fieldset.fieldname).

When modifyMeta() is still needed

switcherConfig covers purely client-side, value-based toggling. As soon as visibility depends on server state - for example "only show the company field for testimonials that already have a company on file, not for new ones" - the modifier from chapter 13 is required, because only PHP knows at load time whether a record exists:

public function modifyMeta(array $meta): array
{
    $isNewRecord = $this->request->getParam('id') === null;

    $meta['general']['children']['company']['arguments']['data']['config']['visible']
        = !$isNewRecord;

    return $meta;
}

imports/exports for data flow between fields

Besides visibility, imports/exports can also declare pure data flow between fields - for example a label that live-updates to reflect the entered customer name:

<field name="testimonial_text" formElement="textarea">
    <settings>
        <imports>
            <link name="label">${ $.provider }:data.customer_name</link>
        </imports>
        <dataType>text</dataType>
        <label translate="true">Testimonial Text</label>
    </settings>
</field>