Steps to reproduce the issue

using a class ComponentnameRule extends FormRule on this path C:\j4dev\htdocs\administrator\components\com_zzzz\src\Rule\ComponentnameRule.php

with xxxxx as vendor and zzzz as component name, I can't make it work.

Expected result

Its work

Actual result

Not work
It always ends with Joomla\CMS\Form\Field\TextField::validate() rule componentname missing.

System information (as much as possible)

Using xampp with php 7.43 running on windows 10.
Joomla_4.0.0-beta1-dev-Development-Full_Package built: Monday, 27 April 2020 02:00:23 UTC

Additional comments

with joomla as vendor and zzzz as component name, its work

From my edit form:

<field
    name="name"
    type="text"
    ...
    validate="componentname"
    required="true"
/>

From top of the validates Rule source:

namespace xxxxx\Component\zzzz\Administrator\Rule;

\defined('_JEXEC') or die;

use Joomla\CMS\Form\FormRule;

/**

• Form Rule class for the Joomla Platform.

*/
class ComponentnameRule extends FormRule
{

Karsten