Month.php

<?php
/**
 * Zend Framework (http://framework.zend.com/)
 *
 * @link      http://github.com/zendframework/zf2 for the canonical source repository
 * @copyright Copyright (c) 2005-2015 Zend Technologies USA Inc. (http://www.zend.com)
 * @license   http://framework.zend.com/license/new-bsd New BSD License
 */

namespace Zend\Form\Element;

use Zend\Validator\DateStep as DateStepValidator;
use Zend\Validator\Regex as RegexValidator;
use Zend\Validator\ValidatorInterface;

class Month extends DateTime
{

    const DATETIME_FORMAT = 'Y-m';

    /**
     * A valid format string accepted by date()
     *
     * @var string
     */
    protected $format = self::DATETIME_FORMAT;

    /**
     * Seed attributes
     *
     * @var array
     */
    protected $attributes = [
        'type' => 'month',
    ];

    /**
     * Retrieves a Date Validator configured for a Month Input type
     *
     * @return ValidatorInterface
     */
    protected function getDateValidator()
    {
        return new RegexValidator('/^[0-9]{4}\-(0[1-9]|1[012])$/');
    }

    /**
     * Retrieves a DateStep Validator configured for a Month Input type
     *
     * @return ValidatorInterface
     */
    protected function getStepValidator()
    {
        $stepValue = (isset($this->attributes['step']))
                     ? $this->attributes['step'] : 1; // Months

        $baseValue = (isset($this->attributes['min']))
                     ? $this->attributes['min'] : '1970-01';

        return new DateStepValidator([
            'format'    => "Y-m",
            'baseValue' => $baseValue,
            'step'      => new \DateInterval("P{$stepValue}M"),
        ]);
    }
}