gistfile1.php

<?php

        $form = new Form();

        $form->setAttribute('method', 'post');

        $fieldset1 = new Fieldset('user');
        $fieldset1->setOptions(array(
                      'use_as_base_fieldset' => true
                  ));

        $fieldset1->add(array(
            'name'       => 'username',
            'type'       => 'Text',
            'options'    => array(
                'label' => 'Username1:'
            )
        ));

        $fieldset2 = new Fieldset('book');
        $fieldset2->setObject(new Book());

        $fieldset2->add(array(
            'name'       => 'name',
            'type'       => 'Zend\Form\Element\Text',
            'options'    => array(
                'label' => 'Buch:'
            )
        ));

        $fieldset1->add($fieldset2);

        $form->add($fieldset1);

        $form->add(array(
            'name'       => 'submit',
            'type'       => 'Zend\Form\Element\Submit',
            'attributes' => array(
                'value' => 'Speichern'
            )
        ));

        $inputFilter = new InputFilter();

        $inputFilter->add(
            array(
                'type' => 'InputFilter',
                array(
                    'name'       => 'username',
                    'validators' => array(
                        array(
                            'name'    => 'StringLength',
                            'options' => array(
                                'min'     => 5,
                                'max'     => 255,
                                'message' => 'Mindestens 5 und maximal 255 Zeichen lang'
                            )
                        )
                    )
                ),
            ),
            'user'
        );

        $form->setInputFilter($inputFilter);