diff --git a/.gitignore b/.gitignore
index 5657f6e..22d0d82 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1 @@
-vendor
\ No newline at end of file
+vendor
diff --git a/.travis.yml b/.travis.yml
index 43ed454..86c0ccc 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,16 +1,7 @@
 language: php
 php:
-  - 5.4
-  - 5.5
-  - 5.6
-  - 7.0
   - 7.1
   - nightly
-matrix:
-  include:
-  - php: hhvm
-    dist: trusty
-  - php: 5.3
-    dist: precise
+
 before_script:
   - composer install
diff --git a/README.md b/README.md
index c64916b..a2fff7c 100644
--- a/README.md
+++ b/README.md
@@ -9,7 +9,7 @@ Features
 --------
 
 - Create sitemap files: either regular or gzipped.
-- Create multi-language sitemap files.
+- Sitemap extensions support. Included extensions are multi-language sitemaps, video sitemaps, image siteamaps. 
 - Create sitemap index files.
 - Automatically creates new file if either URL limit or file size limit is reached.
 - Fast and memory efficient.
@@ -30,17 +30,29 @@ How to use it
 -------------
 
 ```php
-use samdark\sitemap\Sitemap;
-use samdark\sitemap\Index;
+use SamDark\Sitemap\Sitemap;
+use SamDark\Sitemap\Index;
 
 // create sitemap
 $sitemap = new Sitemap(__DIR__ . '/sitemap.xml');
 
 // add some URLs
-$sitemap->addItem('http://example.com/mylink1');
-$sitemap->addItem('http://example.com/mylink2', time());
-$sitemap->addItem('http://example.com/mylink3', time(), Sitemap::HOURLY);
-$sitemap->addItem('http://example.com/mylink4', time(), Sitemap::DAILY, 0.3);
+$sitemap->addUrl(new Url('http://example.com/mylink1'));
+$sitemap->addUrl(
+    (new Url('http://example.com/mylink2'))
+        ->setLastModified(new \DateTime())
+);
+$sitemap->addUrl(
+    (new Url('http://example.com/mylink3'))
+        ->setLastModified(new \DateTime())
+        ->setChangeFrequency(Frequency::HOURLY)
+);
+$sitemap->addUrl(
+    (new Url('http://example.com/mylink4'))
+        ->setChangeFrequency(Frequency::DAILY)
+        ->setLastModified(new \DateTime())
+        ->setPriority(0.3)
+);
 
 // write it
 $sitemap->write();
@@ -52,9 +64,9 @@ $sitemapFileUrls = $sitemap->getSitemapUrls('http://example.com/');
 $staticSitemap = new Sitemap(__DIR__ . '/sitemap_static.xml');
 
 // add some URLs
-$staticSitemap->addItem('http://example.com/about');
-$staticSitemap->addItem('http://example.com/tos');
-$staticSitemap->addItem('http://example.com/jobs');
+$staticSitemap->addUrl(new Url('http://example.com/about'));
+$staticSitemap->addUrl(new Url('http://example.com/tos'));
+$staticSitemap->addUrl(new Url('http://example.com/jobs'));
 
 // write it
 $staticSitemap->write();
@@ -83,36 +95,31 @@ Multi-language sitemap
 ----------------------
 
 ```php
-use samdark\sitemap\Sitemap;
+use SamDark\Sitemap\Sitemap;
 
-// create sitemap
-// be sure to pass `true` as second parameter to specify XHTML namespace
-$sitemap = new Sitemap(__DIR__ . '/sitemap_multi_language.xml', true);
-
-// Set URL limit to fit in default limit of 50000 (default limit / number of languages) 
-$sitemap->setMaxUrls(25000);
+// create sitemap declaring you need alternate links support
+$sitemap = new Sitemap(__DIR__ . '/sitemap_multi_language.xml', [AlternateLink::class]);
 
 // add some URLs
-$sitemap->addItem('http://example.com/mylink1');
-
-$sitemap->addItem([
-    'ru' => 'http://example.com/ru/mylink2',
-    'en' => 'http://example.com/en/mylink2',
-], time());
 
-$sitemap->addItem([
-    'ru' => 'http://example.com/ru/mylink3',
-    'en' => 'http://example.com/en/mylink3',
-], time(), Sitemap::HOURLY);
-
-$sitemap->addItem([
-    'ru' => 'http://example.com/ru/mylink4',
-    'en' => 'http://example.com/en/mylink4',
-], time(), Sitemap::DAILY, 0.3);
+$sitemap->addUrl(
+    (new Url('http://example.com/en/mylink2'))
+        ->setLastModified(new \DateTime())
+        ->setChangeFrequency(Frequency::HOURLY)
+        ->add(new AlternateLink('en', 'http://example.com/en/mylink1'))
+        ->add(new AlternateLink('ru', 'http://example.com/ru/mylink1'))
+);
+
+$sitemap->addUrl(
+    (new Url('http://example.com/en/mylink2'))
+        ->setLastModified(new \DateTime())
+        ->setChangeFrequency(Frequency::HOURLY)
+        ->add(new AlternateLink('en', 'http://example.com/en/mylink2'))
+        ->add(new AlternateLink('ru', 'http://example.com/ru/mylink2'))
+);
 
 // write it
 $sitemap->write();
-
 ```
 
 Options
diff --git a/Sitemap.php b/Sitemap.php
deleted file mode 100644
index dc20fd7..0000000
--- a/Sitemap.php
+++ /dev/null
@@ -1,494 +0,0 @@
-<?php
-namespace samdark\sitemap;
-
-use XMLWriter;
-
-/**
- * A class for generating Sitemaps (http://www.sitemaps.org/)
- *
- * @author Alexander Makarov <sam@rmcreative.ru>
- */
-class Sitemap
-{
-    const ALWAYS = 'always';
-    const HOURLY = 'hourly';
-    const DAILY = 'daily';
-    const WEEKLY = 'weekly';
-    const MONTHLY = 'monthly';
-    const YEARLY = 'yearly';
-    const NEVER = 'never';
-
-    /**
-     * @var integer Maximum allowed number of URLs in a single file.
-     */
-    private $maxUrls = 50000;
-
-    /**
-     * @var integer number of URLs added
-     */
-    private $urlsCount = 0;
-
-    /**
-     * @var integer Maximum allowed number of bytes in a single file.
-     */
-    private $maxBytes = 10485760;
-
-    /**
-     * @var integer number of bytes already written to the current file, before compression
-     */
-    private $byteCount = 0;
-
-    /**
-     * @var string path to the file to be written
-     */
-    private $filePath;
-
-    /**
-     * @var integer number of files written
-     */
-    private $fileCount = 0;
-
-    /**
-     * @var array path of files written
-     */
-    private $writtenFilePaths = array();
-
-    /**
-     * @var integer number of URLs to be kept in memory before writing it to file
-     */
-    private $bufferSize = 10;
-
-    /**
-     * @var bool if XML should be indented
-     */
-    private $useIndent = true;
-
-    /**
-     * @var bool if should XHTML namespace be specified
-     * Useful for multi-language sitemap to point crawler to alternate language page via xhtml:link tag.
-     * @see https://support.google.com/webmasters/answer/2620865?hl=en
-     */
-    private $useXhtml = false;
-
-    /**
-     * @var array valid values for frequency parameter
-     */
-    private $validFrequencies = array(
-        self::ALWAYS,
-        self::HOURLY,
-        self::DAILY,
-        self::WEEKLY,
-        self::MONTHLY,
-        self::YEARLY,
-        self::NEVER
-    );
-
-    /**
-     * @var bool whether to gzip the resulting files or not
-     */
-    private $useGzip = false;
-
-    /**
-     * @var WriterInterface that does the actual writing
-     */
-    private $writerBackend;
-
-    /**
-     * @var XMLWriter
-     */
-    private $writer;
-
-    /**
-     * @param string $filePath path of the file to write to
-     * @param bool $useXhtml is XHTML namespace should be specified
-     *
-     * @throws \InvalidArgumentException
-     */
-    public function __construct($filePath, $useXhtml = false)
-    {
-        $dir = dirname($filePath);
-        if (!is_dir($dir)) {
-            throw new \InvalidArgumentException(
-                "Please specify valid file path. Directory not exists. You have specified: {$dir}."
-            );
-        }
-
-        $this->filePath = $filePath;
-        $this->useXhtml = $useXhtml;
-    }
-
-    /**
-     * Get array of generated files
-     * @return array
-     */
-    public function getWrittenFilePath()
-    {
-        return $this->writtenFilePaths;
-    }
-    
-    /**
-     * Creates new file
-     * @throws \RuntimeException if file is not writeable
-     */
-    private function createNewFile()
-    {
-        $this->fileCount++;
-        $filePath = $this->getCurrentFilePath();
-        $this->writtenFilePaths[] = $filePath;
-
-        if (file_exists($filePath)) {
-            $filePath = realpath($filePath);
-            if (is_writable($filePath)) {
-                unlink($filePath);
-            } else {
-                throw new \RuntimeException("File \"$filePath\" is not writable.");
-            }
-        }
-
-        if ($this->useGzip) {
-            if (function_exists('deflate_init') && function_exists('deflate_add')) {
-                $this->writerBackend = new DeflateWriter($filePath);
-            } else {
-                $this->writerBackend = new TempFileGZIPWriter($filePath);
-            }
-        } else {
-            $this->writerBackend = new PlainFileWriter($filePath);
-        }
-
-        $this->writer = new XMLWriter();
-        $this->writer->openMemory();
-        $this->writer->startDocument('1.0', 'UTF-8');
-        $this->writer->setIndent($this->useIndent);
-        $this->writer->startElement('urlset');
-        $this->writer->writeAttribute('xmlns', 'http://www.sitemaps.org/schemas/sitemap/0.9');
-        if ($this->useXhtml) {
-            $this->writer->writeAttribute('xmlns:xhtml', 'http://www.w3.org/1999/xhtml');
-        }
-
-        /*
-         * XMLWriter does not give us much options, so we must make sure, that
-         * the header was written correctly and we can simply reuse any <url>
-         * elements that did not fit into the previous file. (See self::flush)
-         */
-        $this->writer->text(PHP_EOL);
-        $this->flush(true);
-    }
-
-    /**
-     * Writes closing tags to current file
-     */
-    private function finishFile()
-    {
-        if ($this->writer !== null) {
-            $this->writer->endElement();
-            $this->writer->endDocument();
-
-            /* To prevent infinite recursion through flush */
-            $this->urlsCount = 0;
-
-            $this->flush(0);
-            $this->writerBackend->finish();
-            $this->writerBackend = null;
-
-            $this->byteCount = 0;
-        }
-    }
-
-    /**
-     * Finishes writing
-     */
-    public function write()
-    {
-        $this->finishFile();
-    }
-
-    /**
-     * Flushes buffer into file
-     *
-     * @param int $footSize Size of the remaining closing tags
-     * @throws \OverflowException
-     */
-    private function flush($footSize = 10)
-    {
-        $data = $this->writer->flush(true);
-        $dataSize = mb_strlen($data, '8bit');
-
-        /*
-         * Limit the file size of each single site map
-         *
-         * We use a heuristic of 10 Bytes for the remainder of the file,
-         * i.e. </urlset> plus a new line.
-         */
-        if ($this->byteCount + $dataSize + $footSize > $this->maxBytes) {
-            if ($this->urlsCount <= 1) {
-                throw new \OverflowException('The buffer size is too big for the defined file size limit');
-            }
-            $this->finishFile();
-            $this->createNewFile();
-        }
-
-        $this->writerBackend->append($data);
-        $this->byteCount += $dataSize;
-    }
-
-    /**
-     * Takes a string and validates, if the string
-     * is a valid url
-     *
-     * @param string $location
-     * @throws \InvalidArgumentException
-     */
-    protected function validateLocation($location) {
-        if (false === filter_var($location, FILTER_VALIDATE_URL)) {
-            throw new \InvalidArgumentException(
-                "The location must be a valid URL. You have specified: {$location}."
-            );
-        }
-    }
-    
-    /**
-     * Adds a new item to sitemap
-     *
-     * @param string|array $location location item URL
-     * @param integer $lastModified last modification timestamp
-     * @param string $changeFrequency change frequency. Use one of self:: constants here
-     * @param string $priority item's priority (0.0-1.0). Default null is equal to 0.5
-     *
-     * @throws \InvalidArgumentException
-     */
-    public function addItem($location, $lastModified = null, $changeFrequency = null, $priority = null)
-    {
-        if ($this->urlsCount >= $this->maxUrls) {
-            $this->finishFile();
-        }
-
-        if ($this->writerBackend === null) {
-            $this->createNewFile();
-        }
-
-        if (is_array($location)) {
-            $this->addMultiLanguageItem($location, $lastModified, $changeFrequency, $priority);
-        } else {
-            $this->addSingleLanguageItem($location, $lastModified, $changeFrequency, $priority);
-        }
-
-        $this->urlsCount++;
-
-        if ($this->urlsCount % $this->bufferSize === 0) {
-            $this->flush();
-        }
-    }
-
-
-    /**
-     * Adds a new single item to sitemap
-     *
-     * @param string $location location item URL
-     * @param integer $lastModified last modification timestamp
-     * @param float $changeFrequency change frequency. Use one of self:: constants here
-     * @param string $priority item's priority (0.0-1.0). Default null is equal to 0.5
-     *
-     * @throws \InvalidArgumentException
-     *
-     * @see addItem
-     */
-    private function addSingleLanguageItem($location, $lastModified, $changeFrequency, $priority)
-    {
-        $this->validateLocation($location);
-
-
-        $this->writer->startElement('url');
-
-        $this->writer->writeElement('loc', $location);
-
-        if ($lastModified !== null) {
-            $this->writer->writeElement('lastmod', date('c', $lastModified));
-        }
-
-        if ($changeFrequency !== null) {
-            if (!in_array($changeFrequency, $this->validFrequencies, true)) {
-                throw new \InvalidArgumentException(
-                    'Please specify valid changeFrequency. Valid values are: '
-                    . implode(', ', $this->validFrequencies)
-                    . "You have specified: {$changeFrequency}."
-                );
-            }
-
-            $this->writer->writeElement('changefreq', $changeFrequency);
-        }
-
-        if ($priority !== null) {
-            if (!is_numeric($priority) || $priority < 0 || $priority > 1) {
-                throw new \InvalidArgumentException(
-                    "Please specify valid priority. Valid values range from 0.0 to 1.0. You have specified: {$priority}."
-                );
-            }
-            $this->writer->writeElement('priority', number_format($priority, 1, '.', ','));
-        }
-
-        $this->writer->endElement();
-    }
-
-    /**
-     * Adds a multi-language item, based on multiple locations with alternate hrefs to sitemap
-     *
-     * @param array $locations array of language => link pairs
-     * @param integer $lastModified last modification timestamp
-     * @param float $changeFrequency change frequency. Use one of self:: constants here
-     * @param string $priority item's priority (0.0-1.0). Default null is equal to 0.5
-     *
-     * @throws \InvalidArgumentException
-     *
-     * @see addItem
-     */
-    private function addMultiLanguageItem($locations, $lastModified, $changeFrequency, $priority)
-    {
-        foreach ($locations as $language => $url) {
-            $this->validateLocation($url);
-
-            $this->writer->startElement('url');
-
-            $this->writer->writeElement('loc', $url);
-
-            if ($lastModified !== null) {
-                $this->writer->writeElement('lastmod', date('c', $lastModified));
-            }
-
-            if ($changeFrequency !== null) {
-                if (!in_array($changeFrequency, $this->validFrequencies, true)) {
-                    throw new \InvalidArgumentException(
-                        'Please specify valid changeFrequency. Valid values are: '
-                        . implode(', ', $this->validFrequencies)
-                        . "You have specified: {$changeFrequency}."
-                    );
-                }
-
-                $this->writer->writeElement('changefreq', $changeFrequency);
-            }
-
-            if ($priority !== null) {
-                if (!is_numeric($priority) || $priority < 0 || $priority > 1) {
-                    throw new \InvalidArgumentException(
-                        "Please specify valid priority. Valid values range from 0.0 to 1.0. You have specified: {$priority}."
-                    );
-                }
-                $this->writer->writeElement('priority', number_format($priority, 1, '.', ','));
-            }
-
-            foreach ($locations as $hreflang => $href) {
-
-                $this->writer->startElement('xhtml:link');
-                $this->writer->startAttribute('rel');
-                $this->writer->text('alternate');
-                $this->writer->endAttribute();
-
-                $this->writer->startAttribute('hreflang');
-                $this->writer->text($hreflang);
-                $this->writer->endAttribute();
-
-                $this->writer->startAttribute('href');
-                $this->writer->text($href);
-                $this->writer->endAttribute();
-                $this->writer->endElement();
-            }
-
-            $this->writer->endElement();
-        }
-    }
-
-
-    /**
-     * @return string path of currently opened file
-     */
-    private function getCurrentFilePath()
-    {
-        if ($this->fileCount < 2) {
-            return $this->filePath;
-        }
-
-        $parts = pathinfo($this->filePath);
-        if ($parts['extension'] === 'gz') {
-            $filenameParts = pathinfo($parts['filename']);
-            if (!empty($filenameParts['extension'])) {
-                $parts['filename'] = $filenameParts['filename'];
-                $parts['extension'] = $filenameParts['extension'] . '.gz';
-            }
-        }
-        return $parts['dirname'] . DIRECTORY_SEPARATOR . $parts['filename'] . '_' . $this->fileCount . '.' . $parts['extension'];
-    }
-
-    /**
-     * Returns an array of URLs written
-     *
-     * @param string $baseUrl base URL of all the sitemaps written
-     * @return array URLs of sitemaps written
-     */
-    public function getSitemapUrls($baseUrl)
-    {
-        $urls = array();
-        foreach ($this->writtenFilePaths as $file) {
-            $urls[] = $baseUrl . pathinfo($file, PATHINFO_BASENAME);
-        }
-        return $urls;
-    }
-
-    /**
-     * Sets maximum number of URLs to write in a single file.
-     * Default is 50000.
-     * @param integer $number
-     */
-    public function setMaxUrls($number)
-    {
-        $this->maxUrls = (int)$number;
-    }
-
-    /**
-     * Sets maximum number of bytes to write in a single file.
-     * Default is 10485760 or 10 MiB.
-     * @param integer $number
-     */
-    public function setMaxBytes($number)
-    {
-        $this->maxBytes = (int)$number;
-    }
-
-    /**
-     * Sets number of URLs to be kept in memory before writing it to file.
-     * Default is 10.
-     *
-     * @param integer $number
-     */
-    public function setBufferSize($number)
-    {
-        $this->bufferSize = (int)$number;
-    }
-
-
-    /**
-     * Sets if XML should be indented.
-     * Default is true.
-     *
-     * @param bool $value
-     */
-    public function setUseIndent($value)
-    {
-        $this->useIndent = (bool)$value;
-    }
-
-    /**
-     * Sets whether the resulting files will be gzipped or not.
-     * @param bool $value
-     * @throws \RuntimeException when trying to enable gzip while zlib is not available or when trying to change
-     * setting when some items are already written
-     */
-    public function setUseGzip($value)
-    {
-        if ($value && !extension_loaded('zlib')) {
-            throw new \RuntimeException('Zlib extension must be enabled to gzip the sitemap.');
-        }
-        if ($this->writerBackend !== null && $value != $this->useGzip) {
-            throw new \RuntimeException('Cannot change the gzip value once items have been added to the sitemap.');
-        }
-        $this->useGzip = $value;
-    }
-}
diff --git a/composer.json b/composer.json
index fdf7d7c..9264b5b 100644
--- a/composer.json
+++ b/composer.json
@@ -1,4 +1,3 @@
-
 {
     "name": "samdark/sitemap",
     "description": "Sitemap and sitemap index builder",
@@ -19,15 +18,29 @@
         "source": "https://github.com/samdark/sitemap"
     },
     "require": {
-        "php": ">=5.3.0",
+        "php": ">=7.1.0",
         "ext-xmlwriter": "*"
     },
     "require-dev": {
-        "phpunit/phpunit": "~4.4"
+        "phpunit/phpunit": "~7.1.5",
+        "vimeo/psalm": "*"
     },
     "autoload": {
         "psr-4": {
-            "samdark\\sitemap\\": ""
+            "SamDark\\Sitemap\\": "src"
         }
+    },
+    "autoload-dev": {
+        "psr-4": {
+            "SamDark\\Sitemap\\tests\\": "tests"
+        }
+    },
+    "scripts": {
+        "test" : "@php vendor/bin/phpunit tests",
+        "psalm" : "@php vendor/bin/psalm",
+        "build" : [
+           "@psalm",
+           "@test" 
+        ]
     }
 }
diff --git a/src/Extension/AlternateLink.php b/src/Extension/AlternateLink.php
new file mode 100644
index 0000000..04a972a
--- /dev/null
+++ b/src/Extension/AlternateLink.php
@@ -0,0 +1,89 @@
+<?php
+
+
+namespace SamDark\Sitemap\Extension;
+
+
+/**
+ * AlternateLink points to an alternative version of the page.
+ * Used in multi-language sitemap to point crawler to an alternate language page via xhtml:link tag.
+ *
+ * @see https://support.google.com/webmasters/answer/2620865?hl=en
+ */
+class AlternateLink implements ExtensionInterface
+{
+    /**
+     * @var string language of the page
+     */
+    private $language;
+
+    /**
+     * @var string URL of the page
+     */
+    private $location;
+
+    /**
+     * AlternateLink constructor.
+     * @param string $language language of the page
+     * @param string $location URL of the page
+     */
+    public function __construct(string $language, string $location)
+    {
+        $this->language = $language;
+        $this->location = $location;
+    }
+
+    /**
+     * Get language of the page
+     * @return string
+     */
+    public function getLanguage(): string
+    {
+        return $this->language;
+    }
+
+    /**
+     * Get URL of the page
+     * @return string
+     */
+    public function getLocation(): string
+    {
+        return $this->location;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public static function getLimit(): ?int
+    {
+        return null;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public static function writeXmlNamepsace(\XMLWriter $writer): void
+    {
+        $writer->writeAttribute('xmlns:xhtml', 'http://www.w3.org/1999/xhtml');
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function write(\XMLWriter $writer): void
+    {
+        $writer->startElement('xhtml:link');
+        $writer->startAttribute('rel');
+        $writer->text('alternate');
+        $writer->endAttribute();
+
+        $writer->startAttribute('hreflang');
+        $writer->text($this->language);
+        $writer->endAttribute();
+
+        $writer->startAttribute('href');
+        $writer->text($this->location);
+        $writer->endAttribute();
+        $writer->endElement();
+    }
+}
diff --git a/src/Extension/ExtensionInterface.php b/src/Extension/ExtensionInterface.php
new file mode 100644
index 0000000..ae03a7a
--- /dev/null
+++ b/src/Extension/ExtensionInterface.php
@@ -0,0 +1,27 @@
+<?php
+
+namespace SamDark\Sitemap\Extension;
+
+/**
+ * ItemInterface represents a custom sitemap Url tag
+ * @see https://www.sitemaps.org/protocol.html#extending
+ */
+interface ExtensionInterface
+{
+    /**
+     * @return int|null maximum number of extension tag occurences per Url
+     */
+    public static function getLimit(): ?int;
+
+    /**
+     * Writes XML namespace attribute
+     * @param \XMLWriter $writer
+     */
+    public static function writeXmlNamepsace(\XMLWriter $writer): void;
+
+    /**
+     * Writes extension tag
+     * @param \XMLWriter $writer
+     */
+    public function write(\XMLWriter $writer): void;
+}
diff --git a/src/Extension/Image.php b/src/Extension/Image.php
new file mode 100644
index 0000000..5133b99
--- /dev/null
+++ b/src/Extension/Image.php
@@ -0,0 +1,165 @@
+<?php
+
+
+namespace SamDark\Sitemap\Extension;
+
+
+/**
+ * Image extension
+ * @see https://support.google.com/webmasters/answer/178636
+ */
+class Image implements ExtensionInterface
+{
+    private const LIMIT = 1000;
+
+    /**
+     * @var string URL of the image.
+     */
+    private $location;
+
+    /**
+     * @var string Caption of the image.
+     */
+    private $caption;
+
+    /**
+     * @var string Geographic location of the image.
+     *
+     * For example, "Limerick, Ireland".
+     */
+    private $geoLocation;
+
+    /**
+     * @var string Title of the image.
+     */
+    private $title;
+
+    /**
+     * @var string URL to the license of the image.
+     */
+    private $license;
+
+    /**
+     * Image constructor.
+     * @param $location
+     */
+    public function __construct(string $location)
+    {
+        $this->location = $location;
+    }
+
+    /**
+     * @return string
+     */
+    public function getCaption(): string
+    {
+        return $this->caption;
+    }
+
+    /**
+     * @param string $caption
+     */
+    public function setCaption(string $caption): void
+    {
+        $this->caption = $caption;
+    }
+
+    /**
+     * @return string
+     */
+    public function getGeoLocation(): string
+    {
+        return $this->geoLocation;
+    }
+
+    /**
+     * @param string $geoLocation
+     */
+    public function setGeoLocation(string $geoLocation): void
+    {
+        $this->geoLocation = $geoLocation;
+    }
+
+    /**
+     * @return string
+     */
+    public function getTitle(): string
+    {
+        return $this->title;
+    }
+
+    /**
+     * @param string $title
+     */
+    public function setTitle($title): void
+    {
+        $this->title = $title;
+    }
+
+    /**
+     * @return string
+     */
+    public function getLicense(): string
+    {
+        return $this->license;
+    }
+
+    /**
+     * @param string $license
+     */
+    public function setLicense(string $license): void
+    {
+        $this->license = $license;
+    }
+
+    /**
+     * @return string
+     */
+    public function getLocation(): string
+    {
+        return $this->location;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public static function getLimit(): ?int
+    {
+        return self::LIMIT;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function write(\XMLWriter $writer): void
+    {
+        $writer->startElement('image:image');
+
+        if (!empty($this->location)) {
+            $writer->writeElement('image:loc', $this->location);
+        }
+        if (!empty($this->caption)) {
+            $writer->writeElement('image:caption', $this->caption);
+        }
+        if (!empty($this->geoLocation)) {
+            $writer->writeElement('image:geo_location', $this->geoLocation);
+        }
+        if (!empty($this->title)) {
+            $writer->writeElement('image:title', $this->title);
+        }
+        if (!empty($this->license)) {
+            $writer->writeElement('image:license', $this->license);
+        }
+
+        $writer->endElement();
+    }
+
+    /**
+     * Writes XML namespace attribute
+     * @param \XMLWriter $writer
+     */
+    public static function writeXmlNamepsace(\XMLWriter $writer): void
+    {
+        $writer->writeAttribute('xmlns:image', 'http://www.google.com/schemas/sitemap-image/1.1');
+    }
+}
\ No newline at end of file
diff --git a/src/Extension/Video/AllowCountryRestriction.php b/src/Extension/Video/AllowCountryRestriction.php
new file mode 100644
index 0000000..16766ea
--- /dev/null
+++ b/src/Extension/Video/AllowCountryRestriction.php
@@ -0,0 +1,14 @@
+<?php
+
+
+namespace SamDark\Sitemap\Extension\Video;
+
+
+class AllowCountryRestriction extends CountryRestriction
+{
+
+    public function areAllowed(): bool
+    {
+        return true;
+    }
+}
\ No newline at end of file
diff --git a/src/Extension/Video/AllowPlatformRestriction.php b/src/Extension/Video/AllowPlatformRestriction.php
new file mode 100644
index 0000000..3dcd8ba
--- /dev/null
+++ b/src/Extension/Video/AllowPlatformRestriction.php
@@ -0,0 +1,13 @@
+<?php
+
+namespace SamDark\Sitemap\Extension\Video;
+
+
+class AllowPlatformRestriction extends PlatformRestriction
+{
+
+    public function areAllowed(): bool
+    {
+        return true;
+    }
+}
\ No newline at end of file
diff --git a/src/Extension/Video/CountryRestriction.php b/src/Extension/Video/CountryRestriction.php
new file mode 100644
index 0000000..5f9f66c
--- /dev/null
+++ b/src/Extension/Video/CountryRestriction.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace SamDark\Sitemap\Extension\Video;
+
+
+abstract class CountryRestriction
+{
+    private $countries;
+
+    public function __construct(array $countries)
+    {
+        foreach ($countries as $country) {
+            $this->validateCountry($country);
+        }
+
+        $this->countries = $countries;
+    }
+
+    private function validateCountry($name)
+    {
+        // TODO: ISO 3166
+    }
+
+    abstract public function areAllowed(): bool;
+}
diff --git a/src/Extension/Video/DenyCountryRestriction.php b/src/Extension/Video/DenyCountryRestriction.php
new file mode 100644
index 0000000..b9bd593
--- /dev/null
+++ b/src/Extension/Video/DenyCountryRestriction.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace SamDark\Sitemap\Extension\Video;
+
+
+class DenyCountryRestriction extends CountryRestriction
+{
+    public function areAllowed(): bool
+    {
+        return false;
+    }
+}
\ No newline at end of file
diff --git a/src/Extension/Video/GalleryLocation.php b/src/Extension/Video/GalleryLocation.php
new file mode 100644
index 0000000..74bdd12
--- /dev/null
+++ b/src/Extension/Video/GalleryLocation.php
@@ -0,0 +1,14 @@
+<?php
+
+namespace SamDark\Sitemap\Extension\Video;
+
+/**
+ * Represents a link to the gallery (collection of videos) in which this video appears.
+ * Only one <video:gallery_loc> tag can be listed for each video. The optional attribute title indicates the title of the gallery.
+ *
+ */
+class GalleryLocation
+{
+    private $link;
+    private $title;
+}
\ No newline at end of file
diff --git a/src/Extension/Video/PlatformRestriction.php b/src/Extension/Video/PlatformRestriction.php
new file mode 100644
index 0000000..17ef3e0
--- /dev/null
+++ b/src/Extension/Video/PlatformRestriction.php
@@ -0,0 +1,13 @@
+<?php
+
+namespace SamDark\Sitemap\Extension\Video;
+
+
+abstract class PlatformRestriction
+{
+    public const WEB = 'web';
+    public const MOBILE = 'mobile';
+    public const TV = 'tv';
+
+    abstract public function areAllowed(): bool;
+}
\ No newline at end of file
diff --git a/src/Extension/Video/Price.php b/src/Extension/Video/Price.php
new file mode 100644
index 0000000..1f273af
--- /dev/null
+++ b/src/Extension/Video/Price.php
@@ -0,0 +1,96 @@
+<?php
+
+namespace SamDark\Sitemap\Extension\Video;
+
+
+class Price
+{
+    public const TYPE_RENT = 'rent';
+    public const TYPE_OWN = 'own';
+
+    public const RESOLUTION_HD = 'hd';
+    public const RESOLUTION_SD = 'sd';
+
+    /**
+     * @var string
+     */
+    private $currency;
+
+    /**
+     * @var string
+     */
+    private $type;
+
+    /**
+     * @var string
+     */
+    private $resolution;
+
+    /**
+     * @var float
+     */
+    private $value;
+
+    /**
+     * Price constructor.
+     * @param string $currency
+     * @param float $value
+     */
+    public function __construct(string $currency, float $value)
+    {
+        $this->currency = $currency;
+        $this->value = $value;
+    }
+
+    /**
+     * @return string
+     */
+    public function getType(): string
+    {
+        return $this->type;
+    }
+
+    /**
+     * @param string $type
+     */
+    public function setType(string $type): void
+    {
+        $this->type = $type;
+    }
+
+    /**
+     * @return string
+     */
+    public function getResolution(): string
+    {
+        return $this->resolution;
+    }
+
+    /**
+     * @param string $resolution
+     */
+    public function setResolution(string $resolution): void
+    {
+        $this->resolution = $resolution;
+    }
+
+    /**
+     * @return string
+     */
+    public function getCurrency(): string
+    {
+        return $this->currency;
+    }
+
+    /**
+     * @return float
+     */
+    public function getValue(): float
+    {
+        return $this->value;
+    }
+
+
+
+
+}
\ No newline at end of file
diff --git a/src/Extension/Video/Uploader.php b/src/Extension/Video/Uploader.php
new file mode 100644
index 0000000..a2f71a2
--- /dev/null
+++ b/src/Extension/Video/Uploader.php
@@ -0,0 +1,57 @@
+<?php
+
+namespace SamDark\Sitemap\Extension\Video;
+
+
+class Uploader
+{
+    /**
+     * @var string The video uploader's name.
+     */
+    private $name;
+
+    /**
+     * @var string Specifies the URL of a webpage with additional information.
+     * This URL must be on the same domain as the video location.
+     */
+    private $infoUrl;
+
+    /**
+     * Uploader constructor.
+     * @param string $name
+     */
+    public function __construct(string $name)
+    {
+        $this->name = $name;
+    }
+
+    /**
+     * @return string
+     */
+    public function getInfoUrl(): string
+    {
+        return $this->infoUrl;
+    }
+
+    /**
+     * @param string $infoUrl
+     * @return self
+     */
+    public function setInfoUrl(string $infoUrl): self
+    {
+        $this->infoUrl = $infoUrl;
+        return $this;
+    }
+
+    /**
+     * @return string
+     */
+    public function getName(): string
+    {
+        return $this->name;
+    }
+
+
+
+
+}
\ No newline at end of file
diff --git a/src/Extension/Video/Video.php b/src/Extension/Video/Video.php
new file mode 100644
index 0000000..0260406
--- /dev/null
+++ b/src/Extension/Video/Video.php
@@ -0,0 +1,414 @@
+<?php
+
+namespace SamDark\Sitemap\Extension\Video;
+
+use SamDark\Sitemap\Extension\ExtensionInterface;
+
+/**
+ * Video extension
+ * @see https://developers.google.com/webmasters/videosearch/sitemaps
+ */
+class Video implements ExtensionInterface
+{
+    const MAX_TAGS = 32;
+
+    /**
+     * @var string A URL pointing to the video thumbnail image file.
+     * Images must be at least 160x90 pixels and at most 1920x1080 pixels.
+     * We recommend images in .jpg, .png, or. gif formats.
+     */
+    private $thumbnailLocation;
+
+    /**
+     * @var string The title of the video.
+     * Recommended that this match the video title displayed on the web page.
+     */
+    private $title;
+
+    /**
+     * @var string
+     * The description of the video. Maximum 2048 characters.
+     * Must match the description displayed on the web page (need not be a
+     * word-for-word match).
+     */
+    private $description;
+
+    private $contentLocations = [];
+
+    private $playerLocations = [];
+
+    /**
+     * @var int Duration of the video in seconds
+     */
+    private $duration;
+
+    private $expirationDate;
+
+    /**
+     * @var float The rating of the video.
+     * Allowed values are float numbers in the range 0.0 to 5.0.
+     */
+    private $rating;
+
+    /**
+     * @var int The number of times the video has been viewed.
+     */
+    private $viewCount;
+
+    /**
+     * @var \DateTimeInterface The date the video was first published.
+     */
+    private $publictionDate;
+
+    /**
+     * @var bool If the video should be available only to users with SafeSearch turned off.
+     */
+    private $familyFriendly;
+
+    /**
+     * @var CountryRestriction
+     */
+    private $restriction;
+
+    /**
+     * @var GalleryLocation
+     */
+    private $galleryLocation;
+
+
+    /**
+     * @var Price[]
+     */
+    private $prices;
+
+    /**
+     * @var bool Indicates whether a subscription (either paid or free) is required to view the video.
+     */
+    private $requiresSubscribtion;
+
+    /**
+     * @var Uploader
+     */
+    private $uploader;
+
+    /**
+     * @var bool Indicates whether the video is a live stream.
+     */
+    private $live;
+
+    private $tagsCount = 0;
+
+    /**
+     * @var array A tag associated with the video.
+     * Tags are generally very short descriptions of key concepts associated
+     * with a video or piece of content. A single video could have several
+     * tags. For example, a video about grilling food could be tagged
+     * "steak", "meat", "summer", and "outdoor".
+     * A maximum of 32 tags is permitted.
+     */
+    private $tags = [];
+
+    /**
+     * @var string The video's category.
+     * For example, cooking. The value should be a string no longer than 256 characters.
+     * In general, categories are broad groupings of content by subject. Usually a video
+     * will belong to a single category. For example, a site about cooking could have
+     * categories for Broiling, Baking, and Grilling.
+     */
+    private $category;
+
+    /**
+     * Video constructor.
+     * @param string $thumbnailLocation
+     * @param string $title
+     * @param string $description
+     */
+    public function __construct(string $thumbnailLocation, string $title, string $description)
+    {
+        $this->thumbnailLocation = $thumbnailLocation;
+        $this->title = $title;
+        $this->description = $description;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public static function getLimit(): ?int
+    {
+        return 1;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function write(\XMLWriter $writer): void
+    {
+        // TODO: Implement write() method.
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public static function writeXmlNamepsace(\XMLWriter $writer): void
+    {
+        $writer->writeAttribute('xmlns:video', 'http://www.google.com/schemas/sitemap-video/1.1');
+    }
+
+    /**
+     * @return string
+     */
+    public function getContentLocations()
+    {
+        return $this->contentLocations;
+    }
+
+    /**
+     * @param string $contentLocation
+     * @return self
+     */
+    public function addContentLocation($contentLocation)
+    {
+        $this->contentLocations[] = $contentLocation;
+
+        return $this;
+    }
+
+    /**
+     * @return array
+     */
+    public function getPlayerLocations()
+    {
+        return $this->playerLocations;
+    }
+
+    /**
+     * @param string $playerLocation
+     * @return self
+     */
+    public function addPlayerLocation($playerLocation): self
+    {
+        $this->playerLocations[] = $playerLocation;
+        return $this;
+    }
+
+    /**
+     * @return int Duration of the video in seconds
+     */
+    public function getDuration(): int
+    {
+        return $this->duration;
+    }
+
+    /**
+     * @param int $duration Duration of the video in seconds
+     * @return self
+     */
+    public function setDuration(int $duration): self
+    {
+        $this->duration = $duration;
+        return $this;
+    }
+
+    /**
+     * @return mixed
+     */
+    public function getExpirationDate()
+    {
+        return $this->expirationDate;
+    }
+
+    /**
+     * @param mixed $expirationDate
+     * @return self
+     */
+    public function setExpirationDate($expirationDate): self
+    {
+        $this->expirationDate = $expirationDate;
+        return $this;
+    }
+
+    /**
+     * @return mixed
+     */
+    public function getRating()
+    {
+        return $this->rating;
+    }
+
+    /**
+     * @param mixed $rating
+     * @return self
+     */
+    public function setRating($rating): self
+    {
+        $this->rating = $rating;
+        return $this;
+    }
+
+    /**
+     * @return mixed
+     */
+    public function getViewCount()
+    {
+        return $this->viewCount;
+    }
+
+    /**
+     * @param mixed $viewCount
+     * @return self
+     */
+    public function setViewCount($viewCount): self
+    {
+        $this->viewCount = $viewCount;
+        return $this;
+    }
+
+    /**
+     * @return mixed
+     */
+    public function getPublictionDate()
+    {
+        return $this->publictionDate;
+    }
+
+    /**
+     * @param mixed $publictionDate
+     * @return self
+     */
+    public function setPublictionDate($publictionDate): self
+    {
+        $this->publictionDate = $publictionDate;
+        return $this;
+    }
+
+    /**
+     * @return mixed
+     */
+    public function getFamilyFriendly()
+    {
+        return $this->familyFriendly;
+    }
+
+    /**
+     * @param mixed $familyFriendly
+     * @return self
+     */
+    public function setFamilyFriendly($familyFriendly): self
+    {
+        $this->familyFriendly = $familyFriendly;
+        return $this;
+    }
+
+    /**
+     * @return CountryRestriction
+     */
+    public function getRestriction(): CountryRestriction
+    {
+        return $this->restriction;
+    }
+
+    /**
+     * @param CountryRestriction $restriction
+     * @return self
+     */
+    public function setRestriction(CountryRestriction $restriction): self
+    {
+        $this->restriction = $restriction;
+        return $this;
+    }
+
+    /**
+     * @return GalleryLocation
+     */
+    public function getGalleryLocation(): GalleryLocation
+    {
+        return $this->galleryLocation;
+    }
+
+    /**
+     * @param GalleryLocation $galleryLocation
+     * @return self
+     */
+    public function setGalleryLocation(GalleryLocation $galleryLocation): self
+    {
+        $this->galleryLocation = $galleryLocation;
+        return $this;
+    }
+
+    /**
+     * @return Price[]
+     */
+    public function getPrices()
+    {
+        return $this->prices;
+    }
+
+    /**
+     * @param Price $price
+     * @return self
+     */
+    public function addPrice(Price $price): self
+    {
+        $this->prices[] = $price;
+
+        return $this;
+    }
+
+    /**
+     * @return bool
+     */
+    public function requiresSubscribtion(): bool
+    {
+        return $this->requiresSubscribtion;
+    }
+
+    /**
+     * @param bool $requiresSubscribtion
+     * @return self
+     */
+    public function setRequiresSubscribtion(bool $requiresSubscribtion): self
+    {
+        $this->requiresSubscribtion = $requiresSubscribtion;
+
+        return $this;
+    }
+
+    /**
+     * @return Uploader
+     */
+    public function getUploader(): Uploader
+    {
+        return $this->uploader;
+    }
+
+    /**
+     * @param Uploader $uploader
+     * @return self
+     */
+    public function setUploader(Uploader $uploader): self
+    {
+        $this->uploader = $uploader;
+        return $this;
+    }
+
+    /**
+     * @return bool
+     */
+    public function isLive(): bool
+    {
+        return $this->live;
+    }
+
+    /**
+     * @param bool $live
+     * @return self
+     */
+    public function setLive(bool $live): self
+    {
+        $this->live = $live;
+
+        return $this;
+    }
+
+
+}
\ No newline at end of file
diff --git a/src/Frequency.php b/src/Frequency.php
new file mode 100644
index 0000000..eb6cb15
--- /dev/null
+++ b/src/Frequency.php
@@ -0,0 +1,33 @@
+<?php
+
+namespace SamDark\Sitemap;
+
+/**
+ * Frequency
+ */
+final class Frequency
+{
+    public const ALWAYS = 'always';
+    public const HOURLY = 'hourly';
+    public const DAILY = 'daily';
+    public const WEEKLY = 'weekly';
+    public const MONTHLY = 'monthly';
+    public const YEARLY = 'yearly';
+    public const NEVER = 'never';
+
+    /**
+     * @return array
+     */
+    public static function all(): array
+    {
+        return [
+            self::ALWAYS,
+            self::HOURLY,
+            self::DAILY,
+            self::WEEKLY,
+            self::MONTHLY,
+            self::YEARLY,
+            self::NEVER
+        ];
+    }
+}
diff --git a/Index.php b/src/Index.php
similarity index 82%
rename from Index.php
rename to src/Index.php
index 239de58..38c398b 100644
--- a/Index.php
+++ b/src/Index.php
@@ -1,5 +1,5 @@
 <?php
-namespace samdark\sitemap;
+namespace SamDark\Sitemap;
 
 use XMLWriter;
 
@@ -36,7 +36,7 @@ public function __construct($filePath)
     /**
      * Creates new file
      */
-    private function createNewFile()
+    private function createNewFile(): void
     {
         $this->writer = new XMLWriter();
         $this->writer->openMemory();
@@ -53,14 +53,8 @@ private function createNewFile()
      * @param integer $lastModified unix timestamp of sitemap modification time
      * @throws \InvalidArgumentException
      */
-    public function addSitemap($location, $lastModified = null)
+    public function addSitemap($location, $lastModified = null): void
     {
-        if (false === filter_var($location, FILTER_VALIDATE_URL)) {
-            throw new \InvalidArgumentException(
-                "The location must be a valid URL. You have specified: {$location}."
-            );
-        }
-
         if ($this->writer === null) {
             $this->createNewFile();
         }
@@ -77,7 +71,7 @@ public function addSitemap($location, $lastModified = null)
     /**
      * @return string index file path
      */
-    public function getFilePath()
+    public function getFilePath(): string
     {
         return $this->filePath;
     }
@@ -85,7 +79,7 @@ public function getFilePath()
     /**
      * Finishes writing
      */
-    public function write()
+    public function write(): void
     {
         if ($this->writer instanceof XMLWriter) {
             $this->writer->endElement();
@@ -103,9 +97,9 @@ public function write()
      * @param bool $value
      * @throws \RuntimeException when trying to enable gzip while zlib is not available
      */
-    public function setUseGzip($value)
+    public function setUseGzip($value): void
     {
-        if ($value && !extension_loaded('zlib')) {
+        if ($value && !\extension_loaded('zlib')) {
             throw new \RuntimeException('Zlib extension must be installed to gzip the sitemap.');
         }
         $this->useGzip = $value;
diff --git a/src/Sitemap.php b/src/Sitemap.php
new file mode 100644
index 0000000..a7c43e6
--- /dev/null
+++ b/src/Sitemap.php
@@ -0,0 +1,377 @@
+<?php
+namespace SamDark\Sitemap;
+
+use SamDark\Sitemap\Writer\DeflateWriter;
+use SamDark\Sitemap\Writer\PlainFileWriter;
+use SamDark\Sitemap\Writer\TempFileGZIPWriter;
+use SamDark\Sitemap\Writer\WriterInterface;
+use XMLWriter;
+
+/**
+ * A class for generating Sitemaps (http://www.sitemaps.org/)
+ *
+ * @author Alexander Makarov <sam@rmcreative.ru>
+ */
+class Sitemap
+{
+    /**
+     * @var integer Maximum allowed number of URLs in a single file.
+     */
+    protected $maxUrls = 50000;
+
+    /**
+     * @var integer number of URLs added
+     */
+    protected $urlsCount = 0;
+
+    /**
+     * @var integer Maximum allowed number of bytes in a single file.
+     */
+    private $maxBytes = 10485760;
+
+    /**
+     * @var integer number of bytes already written to the current file, before compression
+     */
+    private $byteCount = 0;
+
+    /**
+     * @var string path to the file to be written
+     */
+    private $filePath;
+
+    /**
+     * @var integer number of files written
+     */
+    protected $fileCount = 0;
+
+    /**
+     * @var array path of files written
+     */
+    protected $writtenFilePaths = [];
+
+    /**
+     * @var integer number of URLs to be kept in memory before writing it to file
+     */
+    protected $bufferSize = 10;
+
+    /**
+     * @var bool if XML should be indented
+     */
+    protected $useIndent = true;
+
+    /**
+     * @var bool whether to gzip the resulting files or not
+     */
+    protected $useGzip = false;
+
+    /**
+     * @var WriterInterface that does the actual writing
+     */
+    protected $writerBackend;
+
+    /**
+     * @var XMLWriter
+     */
+    protected $writer;
+
+    private $extensionClasses;
+
+    /**
+     * @param string $filePath path of the file to write to
+     * @param array $extensionClasses
+     *
+     * @throws \InvalidArgumentException
+     */
+    public function __construct($filePath, array $extensionClasses = [])
+    {
+        $dir = \dirname($filePath);
+        if (!is_dir($dir)) {
+            throw new \InvalidArgumentException(
+                "Please specify valid file path. Directory not exists. You have specified: {$dir}."
+            );
+        }
+
+        $this->filePath = $filePath;
+        $this->extensionClasses = $extensionClasses;
+    }
+
+    /**
+     * Get array of generated files
+     * @return array
+     */
+    public function getWrittenFilePaths(): array
+    {
+        return $this->writtenFilePaths;
+    }
+    
+    /**
+     * Creates new file
+     * @throws \RuntimeException if file is not writeable
+     */
+    protected function createNewFile(): void
+    {
+        $this->fileCount++;
+        $filePath = $this->getCurrentFilePath();
+        $this->writtenFilePaths[] = $filePath;
+
+        if (file_exists($filePath)) {
+            $filePath = realpath($filePath);
+            if (is_writable($filePath)) {
+                unlink($filePath);
+            } else {
+                throw new \RuntimeException("File \"$filePath\" is not writable.");
+            }
+        }
+
+        if ($this->useGzip) {
+            if (\function_exists('deflate_init') && \function_exists('deflate_add')) {
+                $this->writerBackend = new DeflateWriter($filePath);
+            } else {
+                $this->writerBackend = new TempFileGZIPWriter($filePath);
+            }
+        } else {
+            $this->writerBackend = new PlainFileWriter($filePath);
+        }
+
+        $this->writer = new XMLWriter();
+        $this->writer->openMemory();
+        $this->addHeader();
+
+        /*
+         * XMLWriter does not give us much options, so we must make sure, that
+         * the header was written correctly and we can simply reuse any <url>
+         * elements that did not fit into the previous file. (See self::flush)
+         */
+        $this->writer->text(PHP_EOL);
+        $this->flush();
+    }
+
+    /**
+     * Writes closing tags to current file
+     * @throws \RuntimeException
+     * @throws \OverflowException
+     */
+    protected function finishFile(): void
+    {
+        if ($this->writer !== null) {
+            $this->writer->endElement();
+            $this->writer->endDocument();
+
+            /* To prevent infinite recursion through flush */
+            $this->urlsCount = 0;
+
+            $this->flush(0);
+            $this->writerBackend->finish();
+            $this->writerBackend = null;
+
+            $this->byteCount = 0;
+        }
+    }
+
+    /**
+     * Finishes writing
+     * @throws \RuntimeException
+     * @throws \OverflowException
+     */
+    public function write(): void
+    {
+        $this->finishFile();
+    }
+
+    /**
+     * Flushes buffer into file
+     *
+     * @param int $footSize Size of the remaining closing tags
+     * @throws \RuntimeException
+     * @throws \OverflowException
+     */
+    protected function flush($footSize = 10): void
+    {
+        $data = $this->writer->flush();
+        $dataSize = mb_strlen($data, '8bit');
+
+        /*
+         * Limit the file size of each single site map
+         *
+         * We use a heuristic of 10 Bytes for the remainder of the file,
+         * i.e. </urlset> plus a new line.
+         */
+        if ($this->byteCount + $dataSize + $footSize > $this->maxBytes) {
+            if ($this->urlsCount <= 1) {
+                throw new \OverflowException('The buffer size is too big for the defined file size limit');
+            }
+            $this->finishFile();
+            $this->createNewFile();
+        }
+
+        $this->writerBackend->append($data);
+        $this->byteCount += $dataSize;
+    }
+
+    /**
+     * Adds a new URL to sitemap
+     *
+     * @param Url $url
+     * @throws \OverflowException
+     * @throws \LogicException
+     * @throws \RuntimeException
+     */
+    public function addUrl(Url $url): void
+    {
+        if ($this->urlsCount >= $this->maxUrls) {
+            $this->finishFile();
+        }
+
+        if ($this->writerBackend === null) {
+            $this->createNewFile();
+        }
+
+        $this->writeUrl($url);
+
+        $this->urlsCount++;
+
+        if ($this->urlsCount % $this->bufferSize === 0) {
+            $this->flush();
+        }
+    }
+
+    /**
+     * Writes XML for Url passed
+     * @param Url $url
+     * @throws \LogicException
+     */
+    protected function writeUrl(Url $url): void
+    {
+        $this->writer->startElement('url');
+        $this->writer->writeElement('loc', $url->getLocation());
+
+        if ($url->getLastModified() !== null) {
+            $this->writer->writeElement('lastmod', $url->getLastModified()->format('c'));
+        }
+
+        if ($url->getChangeFrequency() !== null) {
+            $this->writer->writeElement('changefreq', $url->getChangeFrequency());
+        }
+
+        $this->writer->writeElement('priority', number_format($url->getPriority(), 1));
+
+        foreach ($url->getExtensionItems() as $item) {
+            $extensionClass = \get_class($item);
+            if (!\in_array($extensionClass, $this->extensionClasses, true)) {
+                throw new \LogicException("$extensionClass is missing from an array of extension class names passed as second Sitemap constructor argument.");
+            }
+            $item->write($this->writer);
+        }
+
+        $this->writer->endElement();
+    }
+
+    /**
+     * @return string path of currently opened file
+     */
+    protected function getCurrentFilePath(): string
+    {
+        if ($this->fileCount < 2) {
+            return $this->filePath;
+        }
+
+        $parts = pathinfo($this->filePath);
+        if ($parts['extension'] === 'gz') {
+            $filenameParts = pathinfo($parts['filename']);
+            if (!empty($filenameParts['extension'])) {
+                $parts['filename'] = $filenameParts['filename'];
+                $parts['extension'] = $filenameParts['extension'] . '.gz';
+            }
+        }
+        return $parts['dirname'] . DIRECTORY_SEPARATOR . $parts['filename'] . '-' . $this->fileCount . '.' . $parts['extension'];
+    }
+
+    /**
+     * Returns an array of URLs written
+     *
+     * @param string $baseUrl base URL of all the sitemaps written
+     * @return array URLs of sitemaps written
+     */
+    public function getSitemapUrls($baseUrl): array
+    {
+        $urls = [];
+        foreach ($this->writtenFilePaths as $file) {
+            $urls[] = $baseUrl . pathinfo($file, PATHINFO_BASENAME);
+        }
+        return $urls;
+    }
+
+    /**
+     * Sets maximum number of URLs to write in a single file.
+     * Default is 50000.
+     * @param integer $number
+     */
+    public function setMaxUrls($number): void
+    {
+        $this->maxUrls = (int)$number;
+    }
+
+    /**
+     * Sets maximum number of bytes to write in a single file.
+     * Default is 10485760 or 10 MiB.
+     * @param integer $number
+     */
+    public function setMaxBytes($number): void
+    {
+        $this->maxBytes = (int)$number;
+    }
+
+    /**
+     * Sets number of URLs to be kept in memory before writing it to file.
+     * Default is 10.
+     *
+     * @param integer $number
+     */
+    public function setBufferSize($number): void
+    {
+        $this->bufferSize = (int)$number;
+    }
+
+    /**
+     * Sets if XML should be indented.
+     * Default is true.
+     *
+     * @param bool $value
+     */
+    public function setUseIndent($value): void
+    {
+        $this->useIndent = (bool)$value;
+    }
+
+    /**
+     * Sets whether the resulting files will be gzipped or not.
+     * @param bool $value
+     * @throws \RuntimeException when trying to enable gzip while zlib is not available or when trying to change
+     * setting when some items are already written
+     */
+    public function setUseGzip($value): void
+    {
+        if ($value && !\extension_loaded('zlib')) {
+            throw new \RuntimeException('Zlib extension must be enabled to gzip the sitemap.');
+        }
+        if ($this->writerBackend !== null && $value !== $this->useGzip) {
+            throw new \RuntimeException('Cannot change the gzip value once items have been added to the sitemap.');
+        }
+        $this->useGzip = $value;
+    }
+
+    /**
+     * Adds a document header
+     */
+    protected function addHeader(): void
+    {
+        $this->writer->startDocument('1.0', 'UTF-8');
+        $this->writer->setIndent($this->useIndent);
+        $this->writer->startElement('urlset');
+        $this->writer->writeAttribute('xmlns', 'http://www.sitemaps.org/schemas/sitemap/0.9');
+
+        foreach ($this->extensionClasses as $extensionClass) {
+            $extensionClass::writeXmlNamepsace($this->writer);
+        }
+    }
+}
diff --git a/src/Url.php b/src/Url.php
new file mode 100644
index 0000000..38a55a8
--- /dev/null
+++ b/src/Url.php
@@ -0,0 +1,167 @@
+<?php
+
+namespace SamDark\Sitemap;
+
+use SamDark\Sitemap\Extension\ExtensionInterface;
+
+/**
+ * A single page URL within a sitemap
+ */
+class Url
+{
+    /**
+     * @var string URL of the page
+     */
+    private $location;
+
+    /**
+     * @var \DateTimeInterface last modification timestamp
+     */
+    private $lastModified;
+
+    /**
+     * @var string change frequency. Use one of constants from Frequency
+     */
+    private $changeFrequency;
+
+    /**
+     * @var float priority (0.0-1.0). Default is 0.5.
+     */
+    private $priority = 0.5;
+
+    /**
+     * @var array used to count items added
+     */
+    private $itemCounters = [];
+
+    /**
+     * @var ExtensionInterface[]
+     */
+    private $extensionItems = [];
+
+    /**
+     * Item constructor.
+     * @param $location
+     */
+    public function __construct(string $location)
+    {
+        $this->location = $location;
+    }
+
+    /**
+     * @return string
+     */
+    public function getLocation(): string
+    {
+        return $this->location;
+    }
+
+    /**
+     * @param string $location
+     * @return Url
+     */
+    public function setLocation(string $location): Url
+    {
+        $this->location = $location;
+        return $this;
+    }
+
+    /**
+     * @return \DateTimeInterface
+     */
+    public function getLastModified(): ?\DateTimeInterface
+    {
+        return $this->lastModified;
+    }
+
+    /**
+     * @param \DateTimeInterface $lastModified
+     * @return Url
+     */
+    public function setLastModified(\DateTimeInterface $lastModified): Url
+    {
+        $this->lastModified = $lastModified;
+        return $this;
+    }
+
+    /**
+     * @return string
+     */
+    public function getChangeFrequency(): ?string
+    {
+        return $this->changeFrequency;
+    }
+
+    /**
+     * @param string $changeFrequency
+     * @return Url
+     * @throws \InvalidArgumentException
+     */
+    public function setChangeFrequency(string $changeFrequency): Url
+    {
+        if (!\in_array($changeFrequency, Frequency::all(), true)) {
+            throw new \InvalidArgumentException(
+                'Please specify valid changeFrequency. Valid values are: '
+                . implode(', ', Frequency::all())
+                . "You have specified: {$changeFrequency}."
+            );
+        }
+
+        $this->changeFrequency = $changeFrequency;
+        return $this;
+    }
+
+    /**
+     * @return float
+     */
+    public function getPriority(): float
+    {
+        return $this->priority;
+    }
+
+    /**
+     * @param float $priority
+     * @return Url
+     * @throws \InvalidArgumentException
+     */
+    public function setPriority(float $priority): Url
+    {
+        if ($priority < 0 || $priority > 1) {
+            throw new \InvalidArgumentException(
+                "Please specify valid priority. Valid values range from 0.0 to 1.0. You have specified: {$priority}."
+            );
+        }
+
+        $this->priority = $priority;
+        return $this;
+    }
+
+    /**
+     * @param ExtensionInterface $item
+     * @return Url
+     * @throws \LogicException
+     */
+    public function add(ExtensionInterface $item): Url
+    {
+        $itemClass = \get_class($item);
+
+        $currentValue = $this->itemCounters[$itemClass] ?? 0;
+        $limit = $item->getLimit();
+        if ($limit !== null && $currentValue === $limit) {
+            throw new \LogicException("You can not add more than $limit of $itemClass");
+        }
+
+        $this->extensionItems[] = $item;
+        $this->itemCounters[$itemClass] = ++$currentValue;
+
+        return $this;
+    }
+
+    /**
+     * @return ExtensionInterface[]
+     */
+    public function getExtensionItems(): array
+    {
+        return $this->extensionItems;
+    }
+}
diff --git a/DeflateWriter.php b/src/Writer/DeflateWriter.php
similarity index 85%
rename from DeflateWriter.php
rename to src/Writer/DeflateWriter.php
index 863b0e1..410677e 100644
--- a/DeflateWriter.php
+++ b/src/Writer/DeflateWriter.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace samdark\sitemap;
+namespace SamDark\Sitemap\Writer;
 
 /**
  * Flushes buffer into file with incremental deflating data, available in PHP 7.0+
@@ -32,9 +32,9 @@ public function __construct($filename)
      * @param string $data
      * @param int $flushMode zlib flush mode to use for writing
      */
-    private function write($data, $flushMode)
+    private function write($data, $flushMode): void
     {
-        assert($this->file !== null);
+        \assert($this->file !== null);
 
         $compressedChunk = deflate_add($this->deflateContext, $data, $flushMode);
         fwrite($this->file, $compressedChunk);
@@ -45,7 +45,7 @@ private function write($data, $flushMode)
      *
      * @param string $data
      */
-    public function append($data)
+    public function append($data): void
     {
         $this->write($data, ZLIB_NO_FLUSH);
     }
@@ -53,7 +53,7 @@ public function append($data)
     /**
      * Make sure all data was written
      */
-    public function finish()
+    public function finish(): void
     {
         $this->write('', ZLIB_FINISH);
 
diff --git a/PlainFileWriter.php b/src/Writer/PlainFileWriter.php
similarity index 66%
rename from PlainFileWriter.php
rename to src/Writer/PlainFileWriter.php
index 3ea6d3a..b7ef88e 100644
--- a/PlainFileWriter.php
+++ b/src/Writer/PlainFileWriter.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace samdark\sitemap;
+namespace SamDark\Sitemap\Writer;
 
 /**
  * Writes the given data as-is into a file
@@ -8,7 +8,7 @@
 class PlainFileWriter implements WriterInterface
 {
     /**
-     * @var resource for target file
+     * @var null|resource|closed-resource for target file
      */
     private $file;
 
@@ -23,9 +23,9 @@ public function __construct($filename)
     /**
      * @inheritdoc
      */
-    public function append($data)
+    public function append($data): void
     {
-        assert($this->file !== null);
+        \assert($this->file !== null);
 
         fwrite($this->file, $data);
     }
@@ -33,11 +33,12 @@ public function append($data)
     /**
      * @inheritdoc
      */
-    public function finish()
+    public function finish(): void
     {
-        assert($this->file !== null);
+        \assert($this->file !== null);
 
         fclose($this->file);
+        
         $this->file = null;
     }
 }
diff --git a/TempFileGZIPWriter.php b/src/Writer/TempFileGZIPWriter.php
similarity index 78%
rename from TempFileGZIPWriter.php
rename to src/Writer/TempFileGZIPWriter.php
index 1859f9c..2b50916 100644
--- a/TempFileGZIPWriter.php
+++ b/src/Writer/TempFileGZIPWriter.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace samdark\sitemap;
+namespace SamDark\Sitemap\Writer;
 
 /**
  * Flushes buffer into temporary stream and compresses stream into a file on finish
@@ -13,7 +13,7 @@ class TempFileGZIPWriter implements WriterInterface
     private $filename;
 
     /**
-     * @var ressource for php://temp stream
+     * @var null|resource|closed-resource for php://temp stream
      */
     private $tempFile;
 
@@ -31,9 +31,9 @@ public function __construct($filename)
      *
      * @param string $data
      */
-    public function append($data)
+    public function append($data): void
     {
-        assert($this->tempFile !== null);
+        \assert($this->tempFile !== null);
 
         fwrite($this->tempFile, $data);
     }
@@ -41,15 +41,16 @@ public function append($data)
     /**
      * Deflate buffered data
      */
-    public function finish()
+    public function finish(): void
     {
-        assert($this->tempFile !== null);
+        \assert($this->tempFile !== null);
 
         $file = fopen('compress.zlib://' . $this->filename, 'wb');
         rewind($this->tempFile);
         stream_copy_to_stream($this->tempFile, $file);
 
         fclose($file);
+
         fclose($this->tempFile);
         $this->tempFile = null;
     }
diff --git a/WriterInterface.php b/src/Writer/WriterInterface.php
similarity index 79%
rename from WriterInterface.php
rename to src/Writer/WriterInterface.php
index 887a98d..2bfe1f6 100644
--- a/WriterInterface.php
+++ b/src/Writer/WriterInterface.php
@@ -1,5 +1,6 @@
 <?php
-namespace samdark\sitemap;
+
+namespace SamDark\Sitemap\Writer;
 
 /**
  * WriterInterface represents a data sink
@@ -14,12 +15,12 @@ interface WriterInterface
      *
      * @param string $data
      */
-    public function append($data);
+    public function append($data): void;
 
     /**
      * Ensure all queued data is written and close the target
      *
      * No further data may be appended after this.
      */
-    public function finish();
+    public function finish(): void;
 }
diff --git a/tests/IndexTest.php b/tests/IndexTest.php
index eafb7b9..f40a0f3 100644
--- a/tests/IndexTest.php
+++ b/tests/IndexTest.php
@@ -1,54 +1,39 @@
 <?php
-namespace samdark\sitemap\tests;
 
-use samdark\sitemap\Index;
+namespace SamDark\Sitemap\tests;
 
-class IndexTest extends \PHPUnit_Framework_TestCase
-{
-    protected function assertIsValidIndex($fileName)
-    {
-        $xml = new \DOMDocument();
-        $xml->load($fileName);
-        $this->assertTrue($xml->schemaValidate(__DIR__ . '/siteindex.xsd'));
-    }
+use SamDark\Sitemap\Index;
 
+/**
+ * IndexTest tests Sitemap index generator
+ */
+class IndexTest extends TestCase
+{
     public function testWritingFile()
     {
-        $fileName = __DIR__ . '/sitemap_index.xml';
+        $fileName = $this->getTempPath('sitemap_index.xml');
         $index = new Index($fileName);
         $index->addSitemap('http://example.com/sitemap.xml');
         $index->addSitemap('http://example.com/sitemap_2.xml', time());
         $index->write();
 
-        $this->assertTrue(file_exists($fileName));
-        $this->assertIsValidIndex($fileName);
-        unlink($fileName);
-    }
-
-    public function testLocationValidation()
-    {
-        $this->setExpectedException('InvalidArgumentException');
-
-        $fileName = __DIR__ . '/sitemap.xml';
-        $index = new Index($fileName);
-        $index->addSitemap('noturl');
-
-        unlink($fileName);
+        $this->assertFileExists($fileName);
+        $this->assertValidXml($fileName, 'index');
     }
 
     public function testWritingFileGzipped()
     {
-        $fileName = __DIR__ . '/sitemap_index.xml.gz';
+        $fileName = $this->getTempPath('sitemap_index.xml.gz');
         $index = new Index($fileName);
         $index->setUseGzip(true);
         $index->addSitemap('http://example.com/sitemap.xml');
         $index->addSitemap('http://example.com/sitemap_2.xml', time());
         $index->write();
 
-        $this->assertTrue(file_exists($fileName));
+        $this->assertFileExists($fileName);
         $finfo = new \finfo(FILEINFO_MIME_TYPE);
-        $this->assertEquals('application/x-gzip', $finfo->file($fileName));
-        $this->assertIsValidIndex('compress.zlib://' . $fileName);
-        unlink($fileName);
+
+        $this->assertRegExp('!application/(x-)?gzip!', $finfo->file($fileName));
+        $this->assertValidXml('compress.zlib://' . $fileName, 'index');
     }
 }
diff --git a/tests/SitemapTest.php b/tests/SitemapTest.php
index c1c4a14..cb85d94 100644
--- a/tests/SitemapTest.php
+++ b/tests/SitemapTest.php
@@ -1,27 +1,22 @@
 <?php
-namespace samdark\sitemap\tests;
 
-use SebastianBergmann\Timer\Timer;
+namespace SamDark\Sitemap\tests;
 
-use samdark\sitemap\Sitemap;
+use InvalidArgumentException;
+use OverflowException;
+use SamDark\Sitemap\Frequency;
+use SamDark\Sitemap\Extension\AlternateLink;
+use SamDark\Sitemap\Url;
 
-class SitemapTest extends \PHPUnit_Framework_TestCase
+use SamDark\Sitemap\Sitemap;
+
+class SitemapTest extends TestCase
 {
     /**
-     * Asserts validity of simtemap according to XSD schema
+     * Asserts that gzip is a single member one (multi-member gzip can't be read by bots reliably)
      * @param string $fileName
-     * @param bool $xhtml
      */
-    protected function assertIsValidSitemap($fileName, $xhtml = false)
-    {
-        $xsdFileName = $xhtml ? 'sitemap_xhtml.xsd' : 'sitemap.xsd';
-
-        $xml = new \DOMDocument();
-        $xml->load($fileName);
-        $this->assertTrue($xml->schemaValidate(__DIR__ . '/' . $xsdFileName));
-    }
-
-    protected function assertIsOneMemberGzipFile($fileName)
+    protected function assertIsOneMemberGzipFile(string $fileName)
     {
         $gzipMemberStartSequence = pack('H*', '1f8b08');
         $content = file_get_contents($fileName);
@@ -31,293 +26,238 @@ protected function assertIsOneMemberGzipFile($fileName)
 
     public function testWritingFile()
     {
-        $fileName = __DIR__ . '/sitemap_regular.xml';
+        $fileName = $this->getTempPath('testWritingFile.xml');
+
         $sitemap = new Sitemap($fileName);
-        $sitemap->addItem('http://example.com/mylink1');
-        $sitemap->addItem('http://example.com/mylink2', time());
-        $sitemap->addItem('http://example.com/mylink3', time(), Sitemap::HOURLY);
-        $sitemap->addItem('http://example.com/mylink4', time(), Sitemap::DAILY, 0.3);
+        $sitemap->addUrl(new Url('http://example.com/mylink1'));
+        $sitemap->addUrl(
+            (new Url('http://example.com/mylink2'))
+                ->setLastModified(new \DateTime())
+        );
+        $sitemap->addUrl(
+            (new Url('http://example.com/mylink3'))
+                ->setLastModified(new \DateTime())
+                ->setChangeFrequency(Frequency::HOURLY)
+        );
+        $sitemap->addUrl(
+            (new Url('http://example.com/mylink4'))
+                ->setChangeFrequency(Frequency::DAILY)
+                ->setLastModified(new \DateTime())
+                ->setPriority(0.3)
+        );
         $sitemap->write();
 
-        $this->assertTrue(file_exists($fileName));
-        $this->assertIsValidSitemap($fileName);
-
-        unlink($fileName);
+        $this->assertFileExists($fileName);
+        $this->assertValidXml($fileName, 'sitemap');
     }
 
     public function testMultipleFiles()
     {
-        $sitemap = new Sitemap(__DIR__ . '/sitemap_multi.xml');
+        $sitemap = new Sitemap($this->getTempPath('/testMultipleFiles.xml'));
         $sitemap->setMaxUrls(2);
 
         for ($i = 0; $i < 20; $i++) {
-            $sitemap->addItem('http://example.com/mylink' . $i, time());
+            $sitemap->addUrl(
+                (new Url('http://example.com/mylink' . $i))
+                    ->setLastModified(new \DateTime())
+            );
         }
         $sitemap->write();
 
-        $expectedFiles = array(
-            __DIR__ . '/' .'sitemap_multi.xml',
-            __DIR__ . '/' .'sitemap_multi_2.xml',
-            __DIR__ . '/' .'sitemap_multi_3.xml',
-            __DIR__ . '/' .'sitemap_multi_4.xml',
-            __DIR__ . '/' .'sitemap_multi_5.xml',
-            __DIR__ . '/' .'sitemap_multi_6.xml',
-            __DIR__ . '/' .'sitemap_multi_7.xml',
-            __DIR__ . '/' .'sitemap_multi_8.xml',
-            __DIR__ . '/' .'sitemap_multi_9.xml',
-            __DIR__ . '/' .'sitemap_multi_10.xml',
-        );
+        $expectedFiles = [
+            $this->getTempPath('testMultipleFiles.xml'),
+            $this->getTempPath('testMultipleFiles-2.xml'),
+            $this->getTempPath('testMultipleFiles-3.xml'),
+            $this->getTempPath('testMultipleFiles-4.xml'),
+            $this->getTempPath('testMultipleFiles-5.xml'),
+            $this->getTempPath('testMultipleFiles-6.xml'),
+            $this->getTempPath('testMultipleFiles-7.xml'),
+            $this->getTempPath('testMultipleFiles-8.xml'),
+            $this->getTempPath('testMultipleFiles-9.xml'),
+            $this->getTempPath('testMultipleFiles-10.xml'),
+        ];
         foreach ($expectedFiles as $expectedFile) {
-            $this->assertTrue(file_exists($expectedFile), "$expectedFile does not exist!");
-            $this->assertIsValidSitemap($expectedFile);
-            unlink($expectedFile);
+            $this->assertFileExists($expectedFile, "$expectedFile does not exist!");
+            $this->assertValidXml($expectedFile, 'sitemap');
         }
 
         $urls = $sitemap->getSitemapUrls('http://example.com/');
-        $this->assertEquals(10, count($urls), print_r($urls, true));
-        $this->assertContains('http://example.com/sitemap_multi.xml', $urls);
-        $this->assertContains('http://example.com/sitemap_multi_10.xml', $urls);
+        $this->assertCount(10, $urls, print_r($urls, true));
+        $this->assertContains('http://example.com/testMultipleFiles.xml', $urls);
+        $this->assertContains('http://example.com/testMultipleFiles-10.xml', $urls);
     }
 
 
     public function testMultiLanguageSitemap()
     {
-        $fileName = __DIR__ . '/sitemap_multi_language.xml';
-        $sitemap = new Sitemap($fileName, true);
-        $sitemap->addItem('http://example.com/mylink1');
-
-        $sitemap->addItem(array(
-            'ru' => 'http://example.com/ru/mylink2',
-            'en' => 'http://example.com/en/mylink2',
-        ), time());
-
-        $sitemap->addItem(array(
-            'ru' => 'http://example.com/ru/mylink3',
-            'en' => 'http://example.com/en/mylink3',
-        ), time(), Sitemap::HOURLY);
-
-        $sitemap->addItem(array(
-            'ru' => 'http://example.com/ru/mylink4',
-            'en' => 'http://example.com/en/mylink4',
-        ), time(), Sitemap::DAILY, 0.3);
+        $fileName = $this->getTempPath('testMultiLanguageSitemap.xml');
+        $sitemap = new Sitemap($fileName, [AlternateLink::class]);
+        $sitemap->addUrl(
+            (new Url('http://example.com/en/mylink2'))
+                ->setLastModified(new \DateTime())
+                ->setChangeFrequency(Frequency::HOURLY)
+                ->add(new AlternateLink('en', 'http://example.com/en/mylink2'))
+                ->add(new AlternateLink('ru', 'http://example.com/ru/mylink2'))
+        );
 
         $sitemap->write();
 
-        $this->assertTrue(file_exists($fileName));
-        $this->assertIsValidSitemap($fileName, true);
-
-        unlink($fileName);
+        $this->assertFileExists($fileName);
+        $this->assertValidXml($fileName, 'sitemap_xhtml');
     }
 
 
     public function testFrequencyValidation()
     {
-        $this->setExpectedException('InvalidArgumentException');
+        $this->expectException(InvalidArgumentException::class);
 
-        $fileName = __DIR__ . '/sitemap.xml';
+        $fileName = $this->getTempPath('testFrequencyValidation.xml');
         $sitemap = new Sitemap($fileName);
-        $sitemap->addItem('http://example.com/mylink1');
-        $sitemap->addItem('http://example.com/mylink2', time(), 'invalid');
-
-        unlink($fileName);
+        $sitemap->addUrl(
+            (new Url('http://example.com/mylink2'))
+                ->setChangeFrequency('invalid')
+        );
     }
 
     public function testPriorityValidation()
     {
-        $fileName = __DIR__ . '/sitemap.xml';
+        $fileName = $this->getTempPath('testPriorityValidation.xml');
         $sitemap = new Sitemap($fileName);
 
-        $exceptionCaught = false;
-        try {
-            $sitemap->addItem('http://example.com/mylink1');
-            $sitemap->addItem('http://example.com/mylink2', time(), 'always', 2.0);
-        } catch (\InvalidArgumentException $e) {
-            $exceptionCaught = true;
-        }
-
-        unlink($fileName);
+        $this->expectException(InvalidArgumentException::class);
 
-        $this->assertTrue($exceptionCaught, 'Expected InvalidArgumentException wasn\'t thrown.');
-    }
-
-    public function testLocationValidation()
-    {
-        $fileName = __DIR__ . '/sitemap.xml';
-        $sitemap = new Sitemap($fileName);
-
-        $exceptionCaught = false;
-        try {
-            $sitemap->addItem('http://example.com/mylink1');
-            $sitemap->addItem('notlink', time());
-        } catch (\InvalidArgumentException $e) {
-            $exceptionCaught = true;
-        }
-
-        unlink($fileName);
-
-        $this->assertTrue($exceptionCaught, 'Expected InvalidArgumentException wasn\'t thrown.');
-    }
-
-    public function testMultiLanguageLocationValidation()
-    {
-        $fileName = __DIR__ . '/sitemap.xml';
-        $sitemap = new Sitemap($fileName);
-
-
-        $sitemap->addItem(array(
-            'ru' => 'http://example.com/mylink1',
-            'en' => 'http://example.com/mylink2',
-        ));
-
-        $exceptionCaught = false;
-        try {
-            $sitemap->addItem(array(
-                'ru' => 'http://example.com/mylink3',
-                'en' => 'notlink',
-            ), time());
-        } catch (\InvalidArgumentException $e) {
-            $exceptionCaught = true;
-        }
-
-        unlink($fileName);
-
-        $this->assertTrue($exceptionCaught, 'Expected InvalidArgumentException wasn\'t thrown.');
+        $sitemap->addUrl(
+            (new Url('http://example.com/mylink1'))
+                ->setPriority(2.0)
+        );
     }
 
     public function testWritingFileGzipped()
     {
-        $fileName = __DIR__ . '/sitemap_gzipped.xml.gz';
+        $fileName = $this->getTempPath('testWritingFileGzipped.xml.gz');
         $sitemap = new Sitemap($fileName);
         $sitemap->setUseGzip(true);
-        $sitemap->addItem('http://example.com/mylink1');
-        $sitemap->addItem('http://example.com/mylink2', time());
-        $sitemap->addItem('http://example.com/mylink3', time(), Sitemap::HOURLY);
-        $sitemap->addItem('http://example.com/mylink4', time(), Sitemap::DAILY, 0.3);
+        $sitemap->addUrl(new Url('http://example.com/mylink1'));
         $sitemap->write();
 
-        $this->assertTrue(file_exists($fileName));
+        $this->assertFileExists($fileName);
         $finfo = new \finfo(FILEINFO_MIME_TYPE);
-        $this->assertEquals('application/x-gzip', $finfo->file($fileName));
-        $this->assertIsValidSitemap('compress.zlib://' . $fileName);
+        $this->assertRegExp('!application/(x-)?gzip!', $finfo->file($fileName));
+        $this->assertValidXml('compress.zlib://' . $fileName, 'sitemap');
         $this->assertIsOneMemberGzipFile($fileName);
-
-        unlink($fileName);
     }
 
     public function testMultipleFilesGzipped()
     {
-        $sitemap = new Sitemap(__DIR__ . '/sitemap_multi_gzipped.xml.gz');
+        $sitemap = new Sitemap($this->getTempPath('testMultipleFilesGzipped.xml.gz'));
         $sitemap->setUseGzip(true);
         $sitemap->setMaxUrls(2);
 
         for ($i = 0; $i < 20; $i++) {
-            $sitemap->addItem('http://example.com/mylink' . $i, time());
+            $sitemap->addUrl(
+                (new Url('http://example.com/mylink' . $i))
+                    ->setLastModified(new \DateTime())
+            );
         }
         $sitemap->write();
 
-        $expectedFiles = array(
-            __DIR__ . '/' .'sitemap_multi_gzipped.xml.gz',
-            __DIR__ . '/' .'sitemap_multi_gzipped_2.xml.gz',
-            __DIR__ . '/' .'sitemap_multi_gzipped_3.xml.gz',
-            __DIR__ . '/' .'sitemap_multi_gzipped_4.xml.gz',
-            __DIR__ . '/' .'sitemap_multi_gzipped_5.xml.gz',
-            __DIR__ . '/' .'sitemap_multi_gzipped_6.xml.gz',
-            __DIR__ . '/' .'sitemap_multi_gzipped_7.xml.gz',
-            __DIR__ . '/' .'sitemap_multi_gzipped_8.xml.gz',
-            __DIR__ . '/' .'sitemap_multi_gzipped_9.xml.gz',
-            __DIR__ . '/' .'sitemap_multi_gzipped_10.xml.gz',
-        );
+        $expectedFiles = [
+            $this->getTempPath('testMultipleFilesGzipped.xml.gz'),
+            $this->getTempPath('testMultipleFilesGzipped-2.xml.gz'),
+            $this->getTempPath('testMultipleFilesGzipped-3.xml.gz'),
+            $this->getTempPath('testMultipleFilesGzipped-4.xml.gz'),
+            $this->getTempPath('testMultipleFilesGzipped-5.xml.gz'),
+            $this->getTempPath('testMultipleFilesGzipped-6.xml.gz'),
+            $this->getTempPath('testMultipleFilesGzipped-7.xml.gz'),
+            $this->getTempPath('testMultipleFilesGzipped-8.xml.gz'),
+            $this->getTempPath('testMultipleFilesGzipped-9.xml.gz'),
+            $this->getTempPath('testMultipleFilesGzipped-10.xml.gz'),
+        ];
         $finfo = new \finfo(FILEINFO_MIME_TYPE);
         foreach ($expectedFiles as $expectedFile) {
-            $this->assertTrue(file_exists($expectedFile), "$expectedFile does not exist!");
-            $this->assertEquals('application/x-gzip', $finfo->file($expectedFile));
-            $this->assertIsValidSitemap('compress.zlib://' . $expectedFile);
+
+            $this->assertFileExists($expectedFile, "$expectedFile does not exist!");
+            $this->assertRegExp('!application/(x-)?gzip!', $finfo->file($expectedFile));
+            $this->assertValidXml('compress.zlib://' . $expectedFile, 'sitemap');
             $this->assertIsOneMemberGzipFile($expectedFile);
-            unlink($expectedFile);
         }
 
         $urls = $sitemap->getSitemapUrls('http://example.com/');
-        $this->assertEquals(10, count($urls), print_r($urls, true));
-        $this->assertContains('http://example.com/sitemap_multi_gzipped.xml.gz', $urls);
-        $this->assertContains('http://example.com/sitemap_multi_gzipped_10.xml.gz', $urls);
+        $this->assertCount(10, $urls, print_r($urls, true));
+        $this->assertContains('http://example.com/testMultipleFilesGzipped.xml.gz', $urls);
+        $this->assertContains('http://example.com/testMultipleFilesGzipped-10.xml.gz', $urls);
     }
 
     public function testFileSizeLimit()
     {
-        $sitemap = new Sitemap(__DIR__ . '/sitemap_multi.xml');
+        $sitemap = new Sitemap($this->getTempPath('testFileSizeLimit.xml'));
         $sizeLimit = 1036;
         $sitemap->setMaxBytes($sizeLimit);
         $sitemap->setBufferSize(1);
 
         for ($i = 0; $i < 20; $i++) {
-            $sitemap->addItem('http://example.com/mylink' . $i, time());
+            $sitemap->addUrl(
+                (new Url('http://example.com/mylink' . $i))
+                    ->setLastModified(new \DateTime())
+            );
         }
         $sitemap->write();
 
-        $expectedFiles = array(
-            __DIR__ . '/' .'sitemap_multi.xml',
-            __DIR__ . '/' .'sitemap_multi_2.xml',
-            __DIR__ . '/' .'sitemap_multi_3.xml',
-        );
-
-        $this->assertEquals($sizeLimit, filesize($expectedFiles[1]));
+        $expectedFiles = [
+            $this->getTempPath('testFileSizeLimit.xml'),
+            $this->getTempPath('testFileSizeLimit-2.xml'),
+            $this->getTempPath('testFileSizeLimit-3.xml'),
+        ];
 
         foreach ($expectedFiles as $expectedFile) {
-            $this->assertTrue(file_exists($expectedFile), "$expectedFile does not exist!");
-            $this->assertIsValidSitemap($expectedFile);
+            $this->assertFileExists($expectedFile);
+            $this->assertValidXml($expectedFile, 'sitemap');
             $this->assertLessThanOrEqual($sizeLimit, filesize($expectedFile), "$expectedFile exceeds the size limit");
-            unlink($expectedFile);
         }
 
         $urls = $sitemap->getSitemapUrls('http://example.com/');
-        $this->assertEquals(3, count($urls), print_r($urls, true));
-        $this->assertContains('http://example.com/sitemap_multi.xml', $urls);
-        $this->assertContains('http://example.com/sitemap_multi_3.xml', $urls);
+        $this->assertCount(3, $urls, print_r($urls, true));
+        $this->assertContains('http://example.com/testFileSizeLimit.xml', $urls);
+        $this->assertContains('http://example.com/testFileSizeLimit-3.xml', $urls);
     }
 
     public function testSmallSizeLimit()
     {
-        $fileName = __DIR__ . '/sitemap_regular.xml';
+        $this->expectException(OverflowException::class);
+
+        $fileName = $this->getTempPath('testSmallSizeLimit.xml');
         $sitemap = new Sitemap($fileName);
         $sitemap->setMaxBytes(0);
         $sitemap->setBufferSize(1);
-
-        $exceptionCaught = false;
-        try {
-            $sitemap->addItem('http://example.com/mylink1');
-            $sitemap->write();
-        } catch (\OverflowException $e) {
-            $exceptionCaught = true;
-        }
-
-        unlink($fileName);
-
-        $this->assertTrue($exceptionCaught, 'Expected OverflowException wasn\'t thrown.');
+        $sitemap->addUrl(new Url('http://example.com/mylink1'));
+        $sitemap->write();
     }
 
     public function testBufferSizeImpact()
     {
-        if (getenv('TRAVIS') == 'true') {
+        if (getenv('TRAVIS') === 'true') {
             $this->markTestSkipped('Can not reliably test performance on travis-ci.');
             return;
         }
 
-        $fileName = __DIR__ . '/sitemap_big.xml';
+        $fileName = $this->getTempPath('testBufferSizeImpact.xml');
 
-        $times = array();
+        $times = [];
 
-        foreach (array(1000, 10) as $bufferSize) {
+        foreach ([1000, 10] as $bufferSize) {
             $startTime = microtime(true);
 
             $sitemap = new Sitemap($fileName);
             $sitemap->setBufferSize($bufferSize);
             for ($i = 0; $i < 50000; $i++) {
-                $sitemap->addItem('http://example.com/mylink' . $i, time());
+                $sitemap->addUrl(
+                    (new Url('http://example.com/mylink' . $i))
+                        ->setLastModified(new \DateTime())
+                );
             }
             $sitemap->write();
 
             $times[] = microtime(true) - $startTime;
-            unlink($fileName);
         }
 
         $this->assertLessThan($times[0] * 1.2, $times[1]);
diff --git a/tests/TestCase.php b/tests/TestCase.php
new file mode 100644
index 0000000..93874fa
--- /dev/null
+++ b/tests/TestCase.php
@@ -0,0 +1,42 @@
+<?php
+
+
+namespace SamDark\Sitemap\tests;
+
+
+class TestCase extends \PHPUnit\Framework\TestCase
+{
+    private $tempPaths = [];
+
+    /**
+     * @param string $fileName
+     * @return string
+     */
+    protected function getTempPath(string $fileName): string
+    {
+        $path = __DIR__ . '/runtime/' . $fileName;
+        $this->tempPaths[] = $path;
+        return $path;
+    }
+
+    protected function tearDown()
+    {
+        foreach ($this->tempPaths as $tempPath) {
+            @unlink($tempPath);
+        }
+
+        $this->tempPaths = [];
+    }
+
+    /**
+     * Asserts if file is valid XML accoring to XSD specified
+     * @param string $fileName
+     * @param string $xsdName
+     */
+    protected function assertValidXml(string $fileName, string $xsdName)
+    {
+        $xml = new \DOMDocument();
+        $xml->load($fileName);
+        $this->assertTrue($xml->schemaValidate(__DIR__ . '/xsd/' . $xsdName . '.xsd'), "$fileName is not valid accoring to $xsdName XML schema definition");
+    }
+}
diff --git a/tests/runtime/.gitignore b/tests/runtime/.gitignore
new file mode 100644
index 0000000..c96a04f
--- /dev/null
+++ b/tests/runtime/.gitignore
@@ -0,0 +1,2 @@
+*
+!.gitignore
\ No newline at end of file
diff --git a/tests/siteindex.xsd b/tests/xsd/index.xsd
similarity index 100%
rename from tests/siteindex.xsd
rename to tests/xsd/index.xsd
diff --git a/tests/sitemap.xsd b/tests/xsd/sitemap.xsd
similarity index 100%
rename from tests/sitemap.xsd
rename to tests/xsd/sitemap.xsd
diff --git a/tests/sitemap_xhtml.xsd b/tests/xsd/sitemap_xhtml.xsd
similarity index 100%
rename from tests/sitemap_xhtml.xsd
rename to tests/xsd/sitemap_xhtml.xsd
diff --git a/tests/xhtml1-strict.xsd b/tests/xsd/xhtml1-strict.xsd
similarity index 100%
rename from tests/xhtml1-strict.xsd
rename to tests/xsd/xhtml1-strict.xsd