class FormTestLimitValidationErrorsForm

class FormTestLimitValidationErrorsForm extends FormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'form_test_limit_validation_errors_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $form['title'] = [
            '#type' => 'textfield',
            '#title' => 'Title',
            '#required' => TRUE,
        ];
        $form['test'] = [
            '#title' => 'Test',
            '#type' => 'textfield',
            '#element_validate' => [
                '::elementValidateLimitValidationErrors',
            ],
        ];
        $form['test_numeric_index'] = [
            '#tree' => TRUE,
        ];
        $form['test_numeric_index'][0] = [
            '#title' => 'Test (numeric index)',
            '#type' => 'textfield',
            '#element_validate' => [
                '::elementValidateLimitValidationErrors',
            ],
        ];
        $form['test_substring'] = [
            '#tree' => TRUE,
        ];
        $form['test_substring']['foo'] = [
            '#title' => 'Test (substring) foo',
            '#type' => 'textfield',
            '#element_validate' => [
                '::elementValidateLimitValidationErrors',
            ],
        ];
        $form['test_substring']['foobar'] = [
            '#title' => 'Test (substring) foobar',
            '#type' => 'textfield',
            '#element_validate' => [
                '::elementValidateLimitValidationErrors',
            ],
        ];
        $form['actions']['partial'] = [
            '#type' => 'submit',
            '#limit_validation_errors' => [
                [
                    'test',
                ],
            ],
            '#submit' => [
                '::partialSubmitForm',
            ],
            '#value' => t('Partial validate'),
        ];
        $form['actions']['partial_numeric_index'] = [
            '#type' => 'submit',
            '#limit_validation_errors' => [
                [
                    'test_numeric_index',
                    0,
                ],
            ],
            '#submit' => [
                '::partialSubmitForm',
            ],
            '#value' => t('Partial validate (numeric index)'),
        ];
        $form['actions']['substring'] = [
            '#type' => 'submit',
            '#limit_validation_errors' => [
                [
                    'test_substring',
                    'foo',
                ],
            ],
            '#submit' => [
                '::partialSubmitForm',
            ],
            '#value' => t('Partial validate (substring)'),
        ];
        $form['actions']['full'] = [
            '#type' => 'submit',
            '#value' => t('Full validate'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function elementValidateLimitValidationErrors($element, FormStateInterface $form_state) {
        if ($element['#value'] == 'invalid') {
            $form_state->setError($element, t('@label element is invalid', [
                '@label' => $element['#title'],
            ]));
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function partialSubmitForm(array &$form, FormStateInterface $form_state) {
        // The title has not been validated, thus its value - in case of the test case
        // an empty string - may not be set.
        if (!$form_state->hasValue('title') && $form_state->hasValue('test')) {
            $this->messenger()
                ->addStatus('Only validated values appear in the form values.');
        }
    }

}