diff --git a/src/Main/Markup/Html/Cdata.php b/src/Main/Markup/Html/Cdata.php
index eca4c79e43..f83d5a18ca 100644
--- a/src/Main/Markup/Html/Cdata.php
+++ b/src/Main/Markup/Html/Cdata.php
@@ -11,64 +11,71 @@
 
 namespace OnPHP\Main\Markup\Html;
 
-use OnPHP\Core\Base\Assert;
-
 /**
  * @ingroup Html
  * @ingroup Module
 **/
 final class Cdata extends SgmlToken
 {
-	private $data	= null;
-
-	private $strict	= false;
+	const CDATA_STRICT_START = '<![CDATA[';
+	const CDATA_STRICT_END = ']]>';
 
 	/**
-	 * @return Cdata
-	**/
-	public static function create()
-	{
-		return new self;
-	}
+	 * @var string|null
+	 */
+	private ?string $data = null;
+	/**
+	 * @var bool
+	 */
+	private bool $strict = false;
 
 	/**
-	 * @return Cdata
-	**/
-	public function setData($data)
+	 * @param string $data
+	 * @return static
+	 */
+	public function setData(string $data): Cdata
 	{
 		$this->data = $data;
 
 		return $this;
 	}
 
-	public function getData()
+	/**
+	 * @return string|null
+	 */
+	public function getData(): ?string
 	{
-		if ($this->strict)
-			return '<![CDATA['.$this->data.']]>';
-		else
+		if ($this->strict) {
+			return self::CDATA_STRICT_START . $this->data . self::CDATA_STRICT_END;
+		} else {
 			return $this->data;
+		}
 	}
 
-	public function getRawData()
+	/**
+	 * @return string|null
+	 */
+	public function getRawData(): ?string
 	{
 		return $this->data;
 	}
 
 	/**
-	 * @return Cdata
-	**/
-	public function setStrict($isStrict)
+	 * @param bool $isStrict
+	 * @return static
+	 */
+	public function setStrict(bool $isStrict): Cdata
 	{
-		Assert::isBoolean($isStrict);
-
 		$this->strict = $isStrict;
 
 		return $this;
 	}
 
-	public function isStrict()
+	/**
+	 * @return bool
+	 */
+	public function isStrict(): bool
 	{
 		return $this->strict;
 	}
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/src/Main/Markup/Html/HtmlAssembler.php b/src/Main/Markup/Html/HtmlAssembler.php
index a6a0c45217..aeb5e3d5af 100644
--- a/src/Main/Markup/Html/HtmlAssembler.php
+++ b/src/Main/Markup/Html/HtmlAssembler.php
@@ -11,6 +11,9 @@
 
 namespace OnPHP\Main\Markup\Html;
 
+use DOMCharacterData;
+use DOMElement;
+use DOMNode;
 use OnPHP\Core\Base\Assert;
 use OnPHP\Core\Exception\WrongArgumentException;
 use OnPHP\Core\Exception\UnimplementedFeatureException;
@@ -20,90 +23,104 @@
 **/
 final class HtmlAssembler
 {
-	private $tags	= null;
-
-	public function __construct($tags)
+	/**
+	 * @var SgmlToken[]
+	 */
+	private array $tags	= [];
+
+	/**
+	 * @param SgmlToken[] $tags
+	 * @throws WrongArgumentException
+	 */
+	public function __construct(array $tags)
 	{
-		Assert::isTrue(current($tags) instanceof SgmlToken);
+		array_map(function ($item) {
+			Assert::isInstance($item, SgmlToken::class);
+		}, $tags ?? []);
 
 		$this->tags = $tags;
 	}
 
+	/**
+	 * @param SgmlToken $tag
+	 * @return string|null
+	 * @throws WrongArgumentException
+	 */
 	public static function makeTag(SgmlToken $tag)
 	{
-		if ($tag instanceof Cdata)
-			$result = $tag->getData();
-		elseif ($tag instanceof SgmlIgnoredTag) {
+		if ($tag instanceof Cdata) {
+			return $tag->getData();
+		} elseif ($tag instanceof SgmlIgnoredTag) {
 			Assert::isNotNull($tag->getId());
 
-			$result = '<'.$tag->getId()
-				.$tag->getCdata()->getData()
+			return '<'.$tag->getId()
+				.($tag->getCdata() instanceof Cdata ? $tag->getCdata()->getData() : '')
 				.$tag->getEndMark().'>';
-
 		} elseif ($tag instanceof SgmlOpenTag) {
 			Assert::isNotNull($tag->getId());
 
 			$attributes = self::getAttributes($tag);
 
-			$result = '<'.$tag->getId()
-				.($attributes ? ' '.$attributes : null)
-				.($tag->isEmpty() ? '/' : null).'>';
-
+			return '<'.$tag->getId()
+				.($attributes ? ' '.$attributes : '')
+				.($tag->isEmpty() ? '/' : '').'>';
 		} elseif ($tag instanceof SgmlEndTag) {
-			$result = '</'.$tag->getId().'>';
+			Assert::isNotNull($tag->getId());
 
-		} else
-			throw new WrongArgumentException(
-				"don't know how to assemble tag class '"
-				.get_class($tag)."'"
-			);
+			return '</'.$tag->getId().'>';
+		}
 
-		return $result;
+		throw new WrongArgumentException(
+			"don't know how to assemble tag class '"
+			.get_class($tag)."'"
+		);
 	}
 
-	public static function makeDomNode(\DOMNode $node)
+	/**
+	 * @param DOMNode $node
+	 * @return string|null
+	 * @throws UnimplementedFeatureException
+	 */
+	public static function makeDomNode(DOMNode $node): ?string
 	{
-			$result = null;
-
-			if ($node instanceof \DOMElement) {
-
-					$result = '<'.$node->nodeName;
+		if ($node instanceof DOMElement) {
+			$result = '<' . $node->nodeName;
+			$attributes = self::getDomAttributes($node);
 
-					$attributes = self::getDomAttributes($node);
-
-					if ($attributes)
-							$result .= ' '.$attributes;
-
-					if (!$node->firstChild) {
-							$result .= ' />';
-					} else {
-							$result .= '>';
-					}
-
-					$childNode = $node->firstChild;
-
-					while ($childNode) {
-							$result .= self::makeDomNode($childNode);
-							$childNode = $childNode->nextSibling;
-					}
-
-					if ($node->firstChild)
-							$result .= '</'.$node->nodeName.'>';
-
-			} elseif ($node instanceof \DOMCharacterData) {
-
-					$result = $node->data;
+			if ($attributes) {
+				$result .= ' ' . $attributes;
+			}
 
+			if (null === $node->firstChild) {
+				$result .= ' />';
 			} else {
-					throw new UnimplementedFeatureException(
-							'assembling of '.get_class($node).' is not implemented yet'
-					);
+				$result .= '>';
 			}
 
+			$childNode = $node->firstChild;
+			while ($childNode) {
+				$result .= self::makeDomNode($childNode);
+				$childNode = $childNode->nextSibling;
+			}
+
+			if ($node->firstChild) {
+				$result .= '</' . $node->nodeName . '>';
+			}
 			return $result;
+		} elseif ($node instanceof DOMCharacterData) {
+			return $node->data;
+		}
+
+		throw new UnimplementedFeatureException(
+			'assembling of '.get_class($node).' is not implemented yet'
+		);
 	}
 
-	public function getHtml()
+	/**
+	 * @return string|null
+	 * @throws WrongArgumentException
+	 */
+	public function getHtml(): ?string
 	{
 		$result = null;
 
@@ -114,43 +131,50 @@ public function getHtml()
 		return $result;
 	}
 
-	private static function getAttributes(SgmlOpenTag $tag)
+	/**
+	 * @param SgmlOpenTag $tag
+	 * @return string
+	 */
+	private static function getAttributes(SgmlOpenTag $tag): string
 	{
 		$attributes = array();
 
 		foreach ($tag->getAttributesList() as $name => $value) {
-			if ($value === null)
-				$quotedValue = null;
-			else
-				// FIXME: is multibyte safe?
-				$quotedValue = '="'.preg_replace('/\"/u', '&quot;', $value).'"';
-
-			$attributes[] = $name.$quotedValue;
+			$attributes[] =
+				$name
+				. (
+					$value === null
+						? ''
+						: '="' . preg_replace('/\"/u', '&quot;', $value) . '"'
+				);
 		}
 
 		return implode(' ', $attributes);
 	}
 
-	private static function getDomAttributes(\DOMNode $node)
+	/**
+	 * @param DOMNode $node
+	 * @return string
+	 */
+	private static function getDomAttributes(DOMNode $node): string
 	{
-		$result = null;
+		if ($node->attributes->length === 0) {
+			return '';
+		}
 
 		$attributes = array();
-
-		if ($node->attributes) {
-			$i = 0;
-
-			while ($item = $node->attributes->item($i)) {
-				$attributes[] = $item->name.'="'.$item->value.'"';
-
-				++$i;
-			}
+		$i = 0;
+
+		while ($item = $node->attributes->item($i++)) {
+			$attributes[] =
+				$item->name
+				. (
+					$item->value
+						? '="' . preg_replace('/\"/u', '&quot;', $item->value) . '"'
+						: ''
+				);
 		}
 
-		if ($attributes)
-			$result = implode(' ', $attributes);
-
-		return $result;
+		return implode(' ', $attributes);
 	}
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/src/Main/Markup/Html/HtmlTokenizer.php b/src/Main/Markup/Html/HtmlTokenizer.php
index fb308fb2d5..fce062a1d0 100644
--- a/src/Main/Markup/Html/HtmlTokenizer.php
+++ b/src/Main/Markup/Html/HtmlTokenizer.php
@@ -11,6 +11,8 @@
 
 namespace OnPHP\Main\Markup\Html;
 
+use OnPHP\Core\Exception\IOException;
+use OnPHP\Core\Exception\WrongArgumentException;
 use OnPHP\Main\Util\IO\InputStream;
 use OnPHP\Core\Base\Assert;
 use OnPHP\Core\Exception\WrongStateException;
@@ -40,16 +42,21 @@ final class HtmlTokenizer
 	const ID_FIRST_CHAR_MASK	= '[A-Za-z]';
 	const ID_CHAR_MASK			= '[-_:.A-Za-z0-9]';
 
-	private $inlineTags			= array('style', 'script', 'textarea');
-
-	private $stream		= null;
+	/**
+	 * @var string[]
+	 */
+	private array $inlineTags       = array('style', 'script', 'textarea');
+	/**
+	 * @var InputStream|null
+	 */
+	private InputStream $stream;
 
-	private $char		= null;
+	private ?string $char           = null;
 
 	// for logging
-	private $line			= 1;
-	private $linePosition	= 1;
-	private $previousChar	= null;
+	private int $line               = 1;
+	private int $linePosition       = 1;
+	private ?string $previousChar   = null;
 
 	private $mark		= null;
 
@@ -76,6 +83,9 @@ final class HtmlTokenizer
 	private $lowercaseAttributes	= false;
 	private $lowercaseTags			= false;
 
+	/**
+	 * @param InputStream $stream
+	 */
 	public function __construct(InputStream $stream)
 	{
 		$this->stream = $stream;
@@ -84,101 +94,126 @@ public function __construct(InputStream $stream)
 	}
 
 	/**
-	 * @return HtmlTokenizer
-	**/
-	public static function create(InputStream $stream)
+	 * @param InputStream $stream
+	 * @return static
+	 */
+	public static function create(InputStream $stream): HtmlTokenizer
 	{
 		return new self($stream);
 	}
 
 	/**
-	 * @return HtmlTokenizer
-	**/
-	public function suppressWhitespaces($isSuppressWhitespaces)
+	 * @param bool $isSuppressWhitespaces
+	 * @return static
+	 */
+	public function suppressWhitespaces(bool $isSuppressWhitespaces): HtmlTokenizer
 	{
-		Assert::isBoolean($isSuppressWhitespaces);
-
 		$this->suppressWhitespaces = $isSuppressWhitespaces;
 
 		return $this;
 	}
 
 	/**
-	 * @return HtmlTokenizer
-	**/
-	public function lowercaseAttributes($isLowercaseAttributes)
+	 * @param bool $isLowercaseAttributes
+	 * @return static
+	 */
+	public function lowercaseAttributes(bool $isLowercaseAttributes): HtmlTokenizer
 	{
-		Assert::isBoolean($isLowercaseAttributes);
-
 		$this->lowercaseAttributes = $isLowercaseAttributes;
 
 		return $this;
 	}
 
 	/**
-	 * @return HtmlTokenizer
-	**/
-	public function lowercaseTags($isLowercaseTags)
+	 * @param bool $isLowercaseTags
+	 * @return static
+	 */
+	public function lowercaseTags(bool $isLowercaseTags): HtmlTokenizer
 	{
-		Assert::isBoolean($isLowercaseTags);
-
 		$this->lowercaseTags = $isLowercaseTags;
 
 		return $this;
 	}
 
 	/**
-	 * @return SgmlToken
-	**/
-	public function nextToken()
+	 * @return SgmlToken|null
+	 * @throws IOException
+	 * @throws WrongArgumentException
+	 * @throws WrongStateException
+	 */
+	public function nextToken(): ?SgmlToken
 	{
-		if ($this->state == self::FINAL_STATE)
+		if ($this->state == self::FINAL_STATE) {
 			return null;
+		}
 
 		$this->completeTag = null;
 
-		while ($this->state != self::FINAL_STATE && !$this->completeTag)
+		while ($this->state != self::FINAL_STATE && !$this->completeTag) {
 			$this->state = $this->handleState();
+		}
 
-		if ($this->state == self::FINAL_STATE && $this->char !== null)
+		if ($this->state == self::FINAL_STATE && $this->char !== null) {
 			throw new WrongStateException('state machine is broken');
-
+		}
 		$this->previousTag = $this->completeTag;
 
 		return $this->completeTag;
 	}
 
-	public function getErrors()
+	/**
+	 * @return array
+	 */
+	public function getErrors(): array
 	{
 		return $this->errors;
 	}
 
-	public static function isIdFirstChar($char)
+	/**
+	 * @param $char
+	 * @return bool
+	 */
+	public static function isIdFirstChar($char): bool
 	{
-		return (preg_match('/'.self::ID_FIRST_CHAR_MASK.'/', $char) > 0);
+		return preg_match('/'.self::ID_FIRST_CHAR_MASK.'/', $char) > 0;
 	}
 
-	public static function isIdChar($char)
+	/**
+	 * @param string $char
+	 * @return bool
+	 */
+	public static function isIdChar(string $char): bool
 	{
-		return (preg_match('/'.self::ID_CHAR_MASK.'/', $char) > 0);
+		return preg_match('/'.self::ID_CHAR_MASK.'/', $char) > 0;
 	}
 
-	public static function isValidId($id)
+	/**
+	 * @param string $id
+	 * @return bool
+	 */
+	public static function isValidId(string $id): bool
 	{
-		$matches = preg_match(
-			'/^'.self::ID_FIRST_CHAR_MASK.self::ID_CHAR_MASK.'*$/',
-			$id
-		);
-
-		return ($matches > 0);
+		return
+			preg_match(
+				'/^'.self::ID_FIRST_CHAR_MASK.self::ID_CHAR_MASK.'*$/',
+				$id
+			) > 0;
 	}
 
-	public static function isSpacerChar($char)
+	/**
+	 * @param string $char
+	 * @return bool
+	 */
+	public static function isSpacerChar(string $char): bool
 	{
-		return (preg_match('/'.self::SPACER_MASK.'/', $char) > 0);
+		return preg_match('/'.self::SPACER_MASK.'/', $char) > 0;
 	}
 
-	public static function removeWhitespaces(Cdata $cdata)
+	/**
+	 * @param Cdata $cdata
+	 * @return Cdata|null
+	 */
+	public static function removeWhitespaces(Cdata $cdata): ?Cdata
 	{
 		$string = $cdata->getData();
 
@@ -187,40 +222,50 @@ public static function removeWhitespaces(Cdata $cdata)
 			' ',
 			$string
 		);
-
 		$string = preg_replace(
 			'/'.self::SPACER_MASK.'+$/',
 			' ',
 			$string
 		);
 
-		if ($string === '' || $string === null)
-			return null;
-
-		$cdata->setData($string);
-
-		return $cdata;
+		return
+			empty($string)
+				? null
+				: $cdata->setData($string);
 	}
 
-	public function isInlineTag($id)
+	/**
+	 * @param string $id
+	 * @return bool
+	 */
+	public function isInlineTag(string $id): bool
 	{
 		return in_array($id, $this->inlineTags);
 	}
 
-	private static function optionalLowercase($string, $ignoreCase)
+	/**
+	 * @param string $string
+	 * @param bool $ignoreCase
+	 * @return string
+	 */
+	private static function optionalLowercase(string $string, bool $ignoreCase): string
 	{
-		if (!$ignoreCase)
-			return $string;
-		else
-			return strtolower($string);
+		return
+			$ignoreCase
+				? mb_strtolower($string)
+				: $string;
 	}
 
-	private function getNextChar()
+	/**
+	 * @return string|null
+	 */
+	private function getNextChar(): ?string
 	{
 		$this->char = $this->stream->read(1);
 
-		if ($this->char === null)
+		if ($this->char === null) {
 			return null;
+		}
 
 		if (
 			$this->char == "\n" && $this->previousChar != "\r"
@@ -231,13 +276,16 @@ private function getNextChar()
 		} else {
 			++$this->linePosition;
 		}
-
 		$this->previousChar = $this->char;
 
 		return $this->char;
 	}
 
-	private function getChars($count)
+	/**
+	 * @param int $count
+	 * @return string|null
+	 */
+	private function getChars(int $count): ?string
 	{
 		$result = null;
 
@@ -253,30 +301,35 @@ private function getChars($count)
 	}
 
 	/**
-	 * @return HtmlTokenizer
-	**/
-	private function mark()
+	 * @return static
+	 */
+	private function mark(): HtmlTokenizer
 	{
 		$this->mark = array(
-			$this->char, $this->previousChar,
-			$this->line, $this->linePosition
+			$this->char,
+			$this->previousChar,
+			$this->line,
+			$this->linePosition
 		);
-
 		$this->stream->mark();
 
 		return $this;
 	}
 
 	/**
-	 * @return HtmlTokenizer
-	**/
-	private function reset()
+	 * @return static
+	 * @throws IOException
+	 * @throws WrongArgumentException
+	 */
+	private function reset(): HtmlTokenizer
 	{
 		Assert::isNotNull($this->mark);
 
 		list (
-			$this->char, $this->previousChar,
-			$this->line, $this->linePosition
+			$this->char,
+			$this->previousChar,
+			$this->line,
+			$this->linePosition
 		) = $this->mark;
 
 		$this->stream->reset();
@@ -285,28 +338,40 @@ private function reset()
 	}
 
 	/**
-	 * @return HtmlTokenizer
-	**/
-	private function skip($count)
+	 * @param int $count
+	 * @return static
+	 */
+	private function skip(int $count): HtmlTokenizer
 	{
-		for ($i = 0; $i < $count; ++$i)
+		for ($i = 0; $i < $count; ++$i) {
 			$this->getNextChar();
+		}
 
 		return $this;
 	}
 
-	private function lookAhead($count)
+	/**
+	 * @param int $count
+	 * @return string
+	 * @throws IOException
+	 */
+	private function lookAhead(int $count): string
 	{
 		$this->stream->mark();
-
 		$result = $this->stream->read($count);
-
 		$this->stream->reset();
 
 		return $result;
 	}
 
-	private function skipString($string, $skipSpaces = false)
+	/**
+	 * @param string $string
+	 * @param bool $skipSpaces
+	 * @return bool
+	 * @throws IOException
+	 * @throws WrongArgumentException
+	 */
+	private function skipString(string $string, bool $skipSpaces = false): bool
 	{
 		$this->mark();
 
@@ -314,14 +379,16 @@ private function skipString($string, $skipSpaces = false)
 			while (
 				$this->char !== null
 				&& self::isSpacerChar($this->char)
-			)
+			) {
 				$this->getNextChar();
+			}
 		}
 
-		$length = strlen($string);
+		$length = mb_strlen($string);
 
-		if ($this->getChars($length) === $string)
+		if ($this->getChars($length) === $string) {
 			return true;
+		}
 
 		$this->reset();
 
@@ -330,22 +397,22 @@ private function skipString($string, $skipSpaces = false)
 
 	/**
 	 * @return HtmlTokenizer
-	**/
-	private function makeTag()
+	 * @throws WrongArgumentException
+	 */
+	private function makeTag(): HtmlTokenizer
 	{
 		Assert::isNotNull($this->tag);
-
 		Assert::isNull($this->attrName);
 		Assert::isNull($this->attrValue);
-
 		Assert::isNull($this->insideQuote);
 
 		if (
 			!$this->suppressWhitespaces
 			|| !$this->tag instanceof Cdata
 			|| (self::removeWhitespaces($this->tag) !== null)
-		)
+		) {
 			$this->tags[] = $this->completeTag = $this->tag;
+		}
 
 		$this->tagId = $this->tag = null;
 
@@ -353,21 +420,28 @@ private function makeTag()
 	}
 
 	/**
+	 * @param SgmlTag $tag
 	 * @return SgmlTag
-	**/
-	private function setupTag(SgmlTag $tag)
+	 * @throws WrongArgumentException
+	 */
+	private function setupTag(SgmlTag $tag): SgmlTag
 	{
 		Assert::isNull($this->tag);
 		Assert::isNotNull($this->tagId);
 
 		$this->tag = $tag->setId($this->tagId);
-
 		$this->tagId = null;
 
 		return $this->tag;
 	}
 
-	private function handleState()
+	/**
+	 * @return int
+	 * @throws IOException
+	 * @throws WrongArgumentException
+	 * @throws WrongStateException
+	 */
+	private function handleState(): int
 	{
 		switch ($this->state) {
 			case self::INITIAL_STATE:
@@ -375,10 +449,11 @@ private function handleState()
 				if (
 					$this->previousTag instanceof SgmlOpenTag
 					&& $this->isInlineTag($this->previousTag->getId())
-				)
+				) {
 					return $this->inlineTagState();
-				else
-					return $this->outsideTagState();
+				}
+
+				return $this->outsideTagState();
 
 			case self::START_TAG_STATE:
 				return $this->startTagState();
@@ -415,25 +490,30 @@ private function handleState()
 	}
 
 	/**
-	 * @return HtmlTokenizer
-	**/
-	private function dumpBuffer()
+	 * @return static
+	 * @throws WrongArgumentException
+	 */
+	private function dumpBuffer(): HtmlTokenizer
 	{
 		if ($this->buffer !== null) {
 			$this->tag = Cdata::create()->setData($this->buffer);
-
 			$this->buffer = null;
-
 			$this->makeTag();
 		}
 
 		return $this;
 	}
 
-	private function checkSpecialTagState()
+	/**
+	 * @return bool|null
+	 * @throws IOException
+	 * @throws WrongArgumentException
+	 */
+	private function checkSpecialTagState(): ?bool
 	{
-		if ($this->char != '!')
+		if ($this->char != '!') {
 			return null;
+		}
 
 		$specialStartTags = array(
 			'![CDATA['	=> self::CDATA_STATE,
@@ -441,34 +521,34 @@ private function checkSpecialTagState()
 		);
 
 		foreach ($specialStartTags as $tag => $state) {
-
-			if ($this->skipString($tag))
+			if ($this->skipString($tag)) {
 				return $state;
+			}
 		}
 
 		return null;
 	}
 
-	// INITIAL_STATE
-	private function outsideTagState()
+	/**
+	 * INITIAL_STATE
+	 * @return int
+	 * @throws IOException
+	 * @throws WrongArgumentException
+	 */
+	private function outsideTagState(): int
 	{
 		Assert::isNull($this->tag);
 		Assert::isNull($this->tagId);
-
 		Assert::isNull($this->attrName);
 		Assert::isNull($this->attrValue);
-
 		Assert::isNull($this->insideQuote);
 
 		while ($this->char !== null) {
 
 			if ($this->char != '<') {
-
 				$this->buffer .= $this->char;
 				$this->getNextChar();
-
 			} else {
-
 				$this->getNextChar();
 
 				if (
@@ -486,29 +566,22 @@ private function outsideTagState()
 					}
 
 					$this->tagId = $this->char;
-
 					$this->getNextChar();
 
 					return self::START_TAG_STATE;
-
 				} elseif ($this->char == '/') {
 					// </
 
-					$this->dumpBuffer();
-
-					$this->getNextChar();
+					$this
+						->dumpBuffer()
+						->getNextChar();
 
 					return self::END_TAG_STATE;
-
 				} else {
 					// <2, <ф, <[space], <>, <[eof]
 
-					$this->warning(
-						'incorrect start-tag, treating it as cdata'
-					);
-
+					$this->warning('incorrect start-tag, treating it as cdata');
 					$this->buffer .= '<'.$this->char;
-
 					$this->getNextChar();
 
 					continue;
@@ -525,41 +598,42 @@ private function outsideTagState()
 
 	/**
 	 * @return SgmlOpenTag
-	**/
-	private function createOpenTag()
+	 * @throws WrongArgumentException
+	 */
+	private function createOpenTag(): SgmlOpenTag
 	{
-		if (!self::isValidId($this->tagId))
+		if (!self::isValidId($this->tagId)) {
 			$this->error("tag id '{$this->tagId}' is invalid");
-		elseif ($this->lowercaseTags)
+		} elseif ($this->lowercaseTags) {
 			$this->tagId = strtolower($this->tagId);
+		}
 
 		return $this->setupTag(SgmlOpenTag::create());
 	}
 
-	// START_TAG_STATE
-	private function startTagState()
+	/**
+	 * START_TAG_STATE
+	 * @return int
+	 * @throws WrongArgumentException
+	 */
+	private function startTagState(): int
 	{
 		Assert::isNull($this->tag);
-		Assert::isNotNull($this->tagId); // strlen(tagId) == 1
-
+		Assert::isNotNull($this->tagId); // mb_strlen(tagId) == 1
 		Assert::isNull($this->attrName);
 		Assert::isNull($this->attrValue);
-
 		Assert::isNull($this->insideQuote);
 
 		while ($this->char !== null) {
-
 			if ($this->char == '>') {
 				// <b>, <divмусор>
 
 				$this->createOpenTag();
-
-				$this->makeTag();
-
-				$this->getNextChar();
+				$this
+					->makeTag()
+					->getNextChar();
 
 				return self::INITIAL_STATE;
-
 			} elseif (self::isSpacerChar($this->char)) {
 				// <p[space], <divмусор[space], <?php[space],
 				// <?xml[space], <!DOCTYPE[space]
@@ -567,7 +641,6 @@ private function startTagState()
 				$externalTag =
 					($this->tagId[0] == '?')
 					&& ($this->tagId != '?xml');
-
 				$doctypeTag = (strtoupper($this->tagId) == '!DOCTYPE');
 
 				if ($externalTag) {
@@ -577,19 +650,20 @@ private function startTagState()
 					);
 				} elseif ($doctypeTag) {
 					$this->setupTag(SgmlIgnoredTag::create());
-				} else
+				} else {
 					$this->createOpenTag();
+				}
 
-				if ($externalTag)
+				if ($externalTag) {
 					return self::EXTERNAL_TAG_STATE;
-				elseif ($doctypeTag)
+				} elseif ($doctypeTag) {
 					return self::DOCTYPE_TAG_STATE;
-				else {
-					// don't eating spacer for external and doctype tags
-					$this->getNextChar();
-
-					return self::INSIDE_TAG_STATE;
 				}
+
+				// don't eating spacer for external and doctype tags
+				$this->getNextChar();
+
+				return self::INSIDE_TAG_STATE;
 			} else {
 				$char = $this->char;
 
@@ -599,10 +673,9 @@ private function startTagState()
 					// <br/>
 
 					$this->createOpenTag()->setEmpty(true);
-
-					$this->makeTag();
-
-					$this->getNextChar();
+					$this
+						->makeTag()
+						->getNextChar();
 
 					return self::INITIAL_STATE;
 				}
@@ -614,77 +687,70 @@ private function startTagState()
 		// ... <tag[end-of-file]
 
 		$this->error('unexpected end of file, tag id is incomplete');
-
 		$this->createOpenTag();
-
 		$this->makeTag();
 
 		return self::FINAL_STATE;
 	}
 
 	/**
-	 * @return HtmlTokenizer
-	**/
-	private function dumpEndTag()
+	 * @return static
+	 * @throws WrongArgumentException
+	 */
+	private function dumpEndTag(): HtmlTokenizer
 	{
 		if (!$this->tagId) {
 			// </>
 			$this->warning('empty end-tag, storing with empty id');
-
 		} elseif (!self::isValidId($this->tagId)) {
-
 			$this->error("end-tag id '{$this->tagId}' is invalid");
 		}
 
-		$this->tag = SgmlEndTag::create()->
-			setId(
-				self::optionalLowercase($this->tagId, $this->lowercaseTags)
-			);
-
+		$this->tag =
+			SgmlEndTag::create()->
+				setId(
+					self::optionalLowercase($this->tagId, $this->lowercaseTags)
+				);
 		$this->makeTag();
 
 		return $this;
 	}
 
-	// END_TAG_STATE
-	private function endTagState()
+	/**
+	 * END_TAG_STATE
+	 * @return int
+	 * @throws WrongArgumentException
+	 */
+	private function endTagState(): int
 	{
 		Assert::isNull($this->tag);
-
 		Assert::isTrue(
 			$this->tagId === null
 			|| $this->char == '>'
 			|| self::isSpacerChar($this->char)
 		);
-
 		Assert::isNull($this->attrName);
 		Assert::isNull($this->attrValue);
-
 		Assert::isNull($this->insideQuote);
 
 		$eatingGarbage = false;
 
 		while ($this->char !== null) {
-
 			if ($this->char == '>') {
 
-				$this->dumpEndTag();
-
-				$this->getNextChar();
+				$this
+					->dumpEndTag()
+					->getNextChar();
 
 				return self::INITIAL_STATE;
-
 			} elseif ($eatingGarbage) {
-
 				$this->getNextChar();
 
 				continue;
-
 			} elseif (self::isSpacerChar($this->char)) {
 				// most browsers parse end-tag until next '>' char
 
 				$eatingGarbage = true;
-
 				$this->getNextChar();
 
 				continue;
@@ -698,66 +764,59 @@ private function endTagState()
 		// ... </[end-of-file], </sometag[eof]
 
 		// NOTE: opera treats </[eof] as cdata, firefox as tag
-		$this->error("unexpected end of file, end-tag is incomplete");
-
-		$this->dumpEndTag();
+		$this
+			->error("unexpected end of file, end-tag is incomplete")
+			->dumpEndTag();
 
 		return self::FINAL_STATE;
 	}
 
-	// INSIDE_TAG_STATE
-	private function insideTagState()
+	/**
+	 * INSIDE_TAG_STATE
+	 * @return int
+	 * @throws WrongArgumentException
+	 */
+	private function insideTagState(): int
 	{
 		Assert::isNull($this->tagId);
-
 		Assert::isNull($this->attrName);
 		Assert::isNull($this->attrValue);
-
 		Assert::isNotNull($this->tag);
-		Assert::isTrue($this->tag instanceof SgmlOpenTag);
-
+		Assert::isInstance($this->tag, SgmlOpenTag::class);
 		Assert::isNull($this->insideQuote);
 
 		while ($this->char !== null) {
-
 			if (self::isSpacerChar($this->char)) {
-				$this->getNextChar();
 
+				$this->getNextChar();
 			} elseif ($this->char == '>') {
 				// <tag ... >
 
-				$this->makeTag();
-
-				$this->getNextChar();
+				$this
+					->makeTag()
+					->getNextChar();
 
 				return self::INITIAL_STATE;
-
 			} elseif ($this->char == '=') {
 
 				// most browsers' behaviour
-				$this->error(
-					'unexpected equal sign, attr name considered empty'
-				);
-
-				$this->getNextChar();
+				$this
+					->error('unexpected equal sign, attr name considered empty')
+					->getNextChar();
 
 				// call?
 				return self::ATTR_VALUE_STATE;
-
 			} else {
-
 				$char = $this->char;
-
 				$this->getNextChar();
 
 				if ($char == '/' && $this->char == '>') {
 					// <tag />, <tag id=value />
 
 					$this->tag->setEmpty(true);
-
-					$this->makeTag();
-
-					$this->getNextChar();
+					$this
+						->makeTag()
+						->getNextChar();
 
 					return self::INITIAL_STATE;
 				}
@@ -771,50 +830,49 @@ private function insideTagState()
 
 		// <tag [eof], <tag id=val [eof]
 
-		$this->error('unexpected end of file, incomplete tag stored');
-
-		$this->makeTag();
+		$this
+			->error('unexpected end of file, incomplete tag stored')
+			->makeTag();
 
 		return self::FINAL_STATE;
 	}
 
 	/**
-	 * @return SgmlOpenTag
-	**/
-	private function dumpAttribute()
+	 * @return static
+	 */
+	private function dumpAttribute(): HtmlTokenizer
 	{
 		if ($this->attrName) {
-
 			if (!self::isValidId($this->attrName))
 				$this->error("attribute name '{$this->attrName}' is invalid");
 			else
 				$this->attrName = strtolower($this->attrName);
-
 		}
 
-		if ($this->attrValue === null || $this->attrValue === '')
+		if ($this->attrValue === null || $this->attrValue === '') {
 			$this->warning("empty value for attr == '{$this->attrName}'");
+		}
 
 		$this->tag->setAttribute($this->attrName, $this->attrValue);
-
 		$this->attrName = $this->attrValue = null;
 
 		return $this;
 	}
 
-	// ATTR_NAME_STATE
-	private function attrNameState()
+	/**
+	 * ATTR_NAME_STATE
+	 * @return int
+	 * @throws WrongArgumentException
+	 */
+	private function attrNameState(): int
 	{
 		Assert::isNotNull($this->tag);
-		Assert::isTrue($this->tag instanceof SgmlOpenTag);
-
+		Assert::isInstance($this->tag,SgmlOpenTag::class);
 		Assert::isNotNull($this->attrName); // length == 1
 		Assert::isNull($this->attrValue);
-
 		Assert::isNull($this->insideQuote);
 
 		while ($this->char !== null) {
-
 			if (self::isSpacerChar($this->char)) {
 				// <tag attr[space]
 
@@ -822,18 +880,15 @@ private function attrNameState()
 
 				// call?
 				return self::WAITING_EQUAL_SIGN_STATE;
-
 			} elseif ($this->char == '>') {
 				// <tag attr>
 
-				$this->dumpAttribute();
-
-				$this->makeTag();
-
-				$this->getNextChar();
+				$this
+					->dumpAttribute()
+					->makeTag()
+					->getNextChar();
 
 				return self::INITIAL_STATE;
-
 			} elseif ($this->char == '=') {
 				// <tag id=
 
@@ -844,9 +899,7 @@ private function attrNameState()
 
 				// call?
 				return self::ATTR_VALUE_STATE;
-
 			} else {
-
 				$char = $this->char;
 
 				$this->getNextChar();
@@ -855,12 +908,10 @@ private function attrNameState()
 					// <option attr=value checked/>
 
 					$this->tag->setEmpty(true);
-
-					$this->dumpAttribute();
-
-					$this->makeTag();
-
-					$this->getNextChar();
+					$this
+						->dumpAttribute()
+						->makeTag()
+						->getNextChar();
 
 					return self::INITIAL_STATE;
 				}
@@ -870,37 +921,35 @@ private function attrNameState()
 		}
 
 		// <tag i[eof]
-
 		// NOTE: opera treats it as cdata, firefox does not
-		$this->dumpAttribute();
-
-		$this->error('unexpected end of file, incomplete tag stored');
-
-		$this->makeTag();
+		$this
+			->dumpAttribute()
+			->error('unexpected end of file, incomplete tag stored')
+			->makeTag();
 
 		return self::FINAL_STATE;
 	}
 
-	// WAITING_EQUAL_SIGN_STATE
-	private function waitingEqualSignState()
+	/**
+	 * WAITING_EQUAL_SIGN_STATE
+	 * @return int
+	 * @throws WrongArgumentException
+	 */
+	private function waitingEqualSignState(): int
 	{
 		Assert::isNotNull($this->tag);
-		Assert::isTrue($this->tag instanceof SgmlOpenTag);
+		Assert::isInstance($this->tag, SgmlOpenTag::class);
 		Assert::isNull($this->tagId);
 		Assert::isNotNull($this->attrName);
 		Assert::isNull($this->attrValue);
-
 		Assert::isNull($this->insideQuote);
 
 		while ($this->char !== null) {
-
 			if (self::isSpacerChar($this->char)) {
 				// <tag attr[space*]
 
 				$this->getNextChar();
-
 			} elseif ($this->char == '=') {
-
 				$this->getNextChar();
 
 				// empty string, not null, to be sure that value needed
@@ -908,7 +957,6 @@ private function waitingEqualSignState()
 
 				// call?
 				return self::ATTR_VALUE_STATE;
-
 			} else {
 				// <tag attr x, <tag attr >
 
@@ -920,22 +968,25 @@ private function waitingEqualSignState()
 
 		// <tag id[space*][eof]
 
-		$this->dumpAttribute();
-
-		$this->error('unexpected end of file, incomplete tag stored');
-
-		$this->makeTag();
+		$this
+			->dumpAttribute()
+			->error('unexpected end of file, incomplete tag stored')
+			->makeTag();
 
 		return self::FINAL_STATE;
 	}
 
-	// ATTR_VALUE_STATE
-	private function attrValueState()
+	/**
+	 * ATTR_VALUE_STATE
+	 * @return int
+	 * @throws IOException
+	 * @throws WrongArgumentException
+	 */
+	private function attrValueState(): int
 	{
 		Assert::isNull($this->tagId);
-
 		Assert::isNotNull($this->tag);
-		Assert::isTrue($this->tag instanceof SgmlOpenTag);
+		Assert::isInstance($this->tag, SgmlOpenTag::class);
 
 		while ($this->char !== null) {
 
@@ -957,14 +1008,12 @@ private function attrValueState()
 			} elseif (!$this->insideQuote && $this->char == '>') {
 				// <tag id=value>, <a href=catalog/>
 
-				$this->dumpAttribute();
-
-				$this->makeTag();
-
-				$this->getNextChar();
+				$this
+					->dumpAttribute()
+					->makeTag()
+					->getNextChar();
 
 				return self::INITIAL_STATE;
-
 			} else {
 				if (
 					$this->char == '"' || $this->char == "'"
@@ -975,27 +1024,22 @@ private function attrValueState()
 						$this->insideQuote = $this->char;
 
 						$this->getNextChar();
-
-						// a place to rollback if second quote will not be
-						// found.
+						// a place to rollback if second quote will not be found.
 						$this->mark();
 
 						continue;
-
 					} elseif ($this->char == $this->insideQuote) {
 						// attr = "value", attr='value', attr='value>([^']*)
 
-						$this->dumpAttribute();
-
-						$this->getNextChar();
+						$this
+							->dumpAttribute()
+							->getNextChar();
 
 						if ($this->insideQuote == '>') {
 							$this->insideQuote = null;
-
 							$this->makeTag();
 
 							return self::INITIAL_STATE;
-
 						} else {
 							$this->insideQuote = null;
 
@@ -1017,16 +1061,14 @@ private function attrValueState()
 			// <tag id="...[eof]
 			//
 			// NOTE: firefox rolls back to the first > after quote.
-			// Opera consideres incomplete tag as cdata.
+			// Opera considers incomplete tag as cdata.
 			// we act as ff does.
 
-			$this->reset();
-
-			$this->warning(
-				"unclosed quoted value for attr == '{$this->attrName}',"
-				." rolling back and searching '>'"
-			);
-
+			$this
+				->reset()
+				->warning(
+					"unclosed quoted value for attr == '{$this->attrName}', rolling back and searching '>'"
+				);
 			$this->attrValue = null;
 			$this->insideQuote = '>';
 
@@ -1037,22 +1079,24 @@ private function attrValueState()
 
 		// <tag id=[space*][eof], <tag id=val[eof]
 
-		$this->dumpAttribute();
-
-		$this->error('unexpected end of file, incomplete tag stored');
-
-		$this->makeTag();
+		$this
+			->dumpAttribute()
+			->error('unexpected end of file, incomplete tag stored')
+			->makeTag();
 
 		return self::FINAL_STATE;
 	}
 
-	// INLINE_TAG_STATE:
-	private function inlineTagState()
+	/**
+	 * INLINE_TAG_STATE
+	 * @return int
+	 * @throws IOException
+	 * @throws WrongArgumentException
+	 */
+	private function inlineTagState(): int
 	{
 		// <script ...>X<-- we are here
-
 		Assert::isNull($this->buffer);
-
 		Assert::isNull($this->tag);
 		Assert::isNull($this->tagId);
 
@@ -1072,9 +1116,9 @@ private function inlineTagState()
 			 * TODO: browsers handles comments in more complex way,
 			 * figure it out
 			**/
-
-			if ($this->skipString('<!--', true))
-				$this->buffer = '<!--'.$this->getComment().'-->';
+			if ($this->skipString('<!--', true)) {
+				$this->buffer = '<!--' . $this->getComment() . '-->';
+			}
 		}
 
 		$endTag = '</'.$startTag;
@@ -1086,37 +1130,33 @@ private function inlineTagState()
 				// </script not found, or found </script[eof]
 
 				break;
-
-			} elseif (
-				$this->char === '>' || self::isSpacerChar($this->char)
-			) {
+			} elseif ($this->char === '>' || self::isSpacerChar($this->char)) {
 				// </script>, </script[space]
 
 				$this->dumpBuffer();
-
 				$this->tagId = $startTag;
 
 				return self::END_TAG_STATE;
 			}
 
 			// </script[any-other-char]
-
 			$this->buffer .= $endTag.$this->char;
 
 			$this->getNextChar();
 		}
 
 		$this->dumpBuffer();
-
-		$this->error(
-			"end-tag for inline tag == '{$startTag}' not found"
-		);
+		$this->error("end-tag for inline tag == '{$startTag}' not found");
 
 		return self::FINAL_STATE;
 	}
 
-	// CDATA_STATE
-	private function cdataState()
+	/**
+	 * CDATA_STATE
+	 * @return int
+	 * @throws WrongArgumentException
+	 */
+	private function cdataState(): int
 	{
 		Assert::isNull($this->tag);
 		Assert::isNull($this->tagId);
@@ -1131,7 +1171,6 @@ private function cdataState()
 		$this->makeTag();
 
 		if (!$this->substringFound) {
-
 			$this->error('unexpected end-of-file inside cdata tag');
 
 			return self::FINAL_STATE;
@@ -1140,7 +1179,12 @@ private function cdataState()
 		return self::INITIAL_STATE;
 	}
 
-	private function getComment()
+	/**
+	 * @return string
+	 * @throws IOException
+	 * @throws WrongArgumentException
+	 */
+	private function getComment(): string
 	{
 		$this->mark();
 
@@ -1149,86 +1193,82 @@ private function getComment()
 		if (!$this->substringFound) {
 			$this->reset();
 
-			$this->error(
-				'unexpected end-of-file inside comment tag,'
-				." trying to find '>'"
-			);
+			$this->error("unexpected end-of-file inside comment tag, trying to find '>'");
 
 			$result = $this->getContentToSubstring('>');
 
-			if (!$this->substringFound)
-				$this->error(
-					"end-tag '>' not found,"
-					.' treating all remaining content as cdata'
-				);
+			if (!$this->substringFound) {
+				$this->error("end-tag '>' not found, treating all remaining content as cdata");
+			}
 		}
 
 		return $result;
 	}
 
-	// COMMENT_STATE
-	private function commentState()
+	/**
+	 * COMMENT_STATE
+	 * @return int
+	 * @throws IOException
+	 * @throws WrongArgumentException
+	 */
+	private function commentState(): int
 	{
 		Assert::isNull($this->tag);
 		Assert::isNull($this->tagId);
 
 		$content = $this->getComment();
-
-		$this->tag =
-			SgmlIgnoredTag::comment()->
-			setCdata(
-				Cdata::create()->setData($content)
-			);
-
+		$this->tag = SgmlIgnoredTag::comment()
+			->setCdata(Cdata::create()->setData($content));
 		$this->makeTag();
 
 		return self::INITIAL_STATE;
 	}
 
-	// EXTERNAL_TAG_STATE:
-	private function externalTagState()
+	/**
+	 * EXTERNAL_TAG_STATE:
+	 * @return int
+	 * @throws IOException
+	 * @throws WrongArgumentException
+	 */
+	private function externalTagState(): int
 	{
 		Assert::isTrue($this->tag instanceof SgmlIgnoredTag);
 
 		$this->mark();
-
 		$content = $this->getContentToSubstring('?>');
 
 		if (!$this->substringFound) {
 			$this->reset();
 
-			$this->error(
-				'unexpected end-of-file inside external tag,'
-				." trying to find '>'"
-			);
-
+			$this->error("unexpected end-of-file inside external tag, trying to find '>'");
 			$content = $this->getContentToSubstring('>');
 
-			if (!$this->substringFound)
-				$this->error(
-					"end-tag '>' not found,"
-					.' treating all remaining content as cdata'
-				);
+			if (!$this->substringFound) {
+				$this->error("end-tag '>' not found, treating all remaining content as cdata");
+			}
 		}
 
 		$this->tag->setCdata(Cdata::create()->setData($content));
-
 		$this->makeTag();
 
 		return self::INITIAL_STATE;
 	}
 
-	// DOCTYPE_TAG_STATE:
-	private function doctypeTagState()
+	/**
+	 * DOCTYPE_TAG_STATE:
+	 * @return int
+	 * @throws WrongArgumentException
+	 * @todo use DoctypeTag and parse it correctly as Opera does and Firefox does not.
+	 */
+	private function doctypeTagState(): int
 	{
-		// TODO: use DoctypeTag and parse it correctly as Opera does and
-		// Firefox does not.
 		Assert::isTrue($this->tag instanceof SgmlIgnoredTag);
 
 		$content = $this->getContentToSubstring('>');
 
-		if (!$this->substringFound)
+		if (!$this->substringFound) {
 			$this->error('unexpected end-of-file inside doctype tag');
+		}
 
 		$this->tag->setCdata(Cdata::create()->setData($content));
 
@@ -1239,14 +1279,16 @@ private function doctypeTagState()
 
 	/**
 	 * using Knuth-Morris-Pratt algorithm.
-	 * 
 	 * If $substring not found, returns whole remaining content
-	**/
-	private function getContentToSubstring($substring, $ignoreCase = false)
+	 * @param string $substring
+	 * @param bool $ignoreCase
+	 * @return string
+	 */
+	private function getContentToSubstring(string $substring, bool $ignoreCase = false): string
 	{
 		$this->substringFound = false;
 
-		$substringLength = strlen($substring);
+		$substringLength = mb_strlen($substring);
 
 		$prefixTable = array(1 => 0);
 		$buffer = $substring."\x00";
@@ -1254,21 +1296,19 @@ private function getContentToSubstring($substring, $ignoreCase = false)
 
 		while ($this->char !== null) {
 
-			if ($i < $substringLength)
+			if ($i < $substringLength) {
 				$char = $buffer[$i + 1];
-			else {
+			} else {
 				$char = $this->char;
 				$buffer .= $char;
 				$this->getNextChar();
 			}
 
 			$maxLength = $prefixTable[$i + 1];
-
 			$char = self::optionalLowercase($char, $ignoreCase);
 
 			while (
-				self::optionalLowercase($buffer[$maxLength], $ignoreCase)
-					!== $char
+				self::optionalLowercase($buffer[$maxLength], $ignoreCase) !== $char
 				&& $maxLength > 0
 			) {
 				$maxLength = $prefixTable[$maxLength];
@@ -1277,10 +1317,7 @@ private function getContentToSubstring($substring, $ignoreCase = false)
 			++$i;
 
 			$prefixTable[$i + 1] =
-				(
-					self::optionalLowercase($buffer[$maxLength], $ignoreCase)
-						=== $char
-				)
+				self::optionalLowercase($buffer[$maxLength], $ignoreCase) === $char
 					? $maxLength + 1
 					: 0;
 
@@ -1294,17 +1331,17 @@ private function getContentToSubstring($substring, $ignoreCase = false)
 			}
 		}
 
-		if (!$this->substringFound)
-			return substr(
-				$buffer, $substringLength + 1
-			);
-		else
-			return substr(
-				$buffer, $substringLength + 1, $i - 2 * $substringLength
-			);
+		if (!$this->substringFound) {
+			return mb_substr($buffer, $substringLength + 1);
+		} else {
+			return mb_substr($buffer, $substringLength + 1, $i - 2 * $substringLength);
+		}
 	}
 
-	private function getTextualPosition()
+	/**
+	 * @return string
+	 */
+	private function getTextualPosition(): string
 	{
 		return
 			"line {$this->line}, position {$this->linePosition}"
@@ -1316,25 +1353,26 @@ private function getTextualPosition()
 	}
 
 	/**
+	 * @param string $message
 	 * @return HtmlTokenizer
-	**/
-	private function warning($message)
+	 */
+	private function warning(string $message): HtmlTokenizer
 	{
 		$this->errors[] =
-			"warning at {$this->getTextualPosition()}: $message";
+			"warning at {$this->getTextualPosition()}: {$message}";
 
 		return $this;
 	}
 
 	/**
+	 * @param string $message
 	 * @return HtmlTokenizer
-	**/
-	private function error($message)
+	 */
+	private function error(string $message): HtmlTokenizer
 	{
 		$this->errors[] =
 			"error at {$this->getTextualPosition()}: $message";
 
 		return $this;
 	}
-}
-?>
+}
\ No newline at end of file
diff --git a/src/Main/Markup/Html/SgmlEndTag.php b/src/Main/Markup/Html/SgmlEndTag.php
index 2d88bf5bd8..916ef2fc04 100644
--- a/src/Main/Markup/Html/SgmlEndTag.php
+++ b/src/Main/Markup/Html/SgmlEndTag.php
@@ -15,14 +15,4 @@
  * @ingroup Html
  * @ingroup Module
 **/
-final class SgmlEndTag extends SgmlTag
-{
-	/**
-	 * @return SgmlEndTag
-	**/
-	public static function create()
-	{
-		return new self;
-	}
-}
-?>
\ No newline at end of file
+final class SgmlEndTag extends SgmlTag { /**  */ }
\ No newline at end of file
diff --git a/src/Main/Markup/Html/SgmlIgnoredTag.php b/src/Main/Markup/Html/SgmlIgnoredTag.php
index 3a8df5cc75..06fd4c133d 100644
--- a/src/Main/Markup/Html/SgmlIgnoredTag.php
+++ b/src/Main/Markup/Html/SgmlIgnoredTag.php
@@ -16,29 +16,28 @@
 **/
 final class SgmlIgnoredTag extends SgmlTag
 {
-	private $cdata		= null;
-	private $endMark	= null;
-
 	/**
-	 * @return SgmlIgnoredTag
-	**/
-	public static function create()
-	{
-		return new self;
-	}
+	 * @var Cdata|null
+	 */
+	private ?Cdata $cdata = null;
+	/**
+	 * @var string|null
+	 */
+	private ?string $endMark = null;
 
 	/**
-	 * @return SgmlIgnoredTag
-	**/
-	public static function comment()
+	 * @return static
+	 */
+	public static function comment(): SgmlIgnoredTag
 	{
 		return self::create()->setId('!--')->setEndMark('--');
 	}
 
 	/**
-	 * @return SgmlIgnoredTag
-	**/
-	public function setCdata(Cdata $cdata)
+	 * @param Cdata $cdata
+	 * @return static
+	 */
+	public function setCdata(Cdata $cdata): SgmlIgnoredTag
 	{
 		$this->cdata = $cdata;
 
@@ -46,36 +45,45 @@ public function setCdata(Cdata $cdata)
 	}
 
 	/**
-	 * @return Cdata
-	**/
-	public function getCdata()
+	 * @return Cdata|null
+	 */
+	public function getCdata(): ?Cdata
 	{
 		return $this->cdata;
 	}
 
 	/**
-	 * @return SgmlIgnoredTag
-	**/
-	public function setEndMark($endMark)
+	 * @param string $endMark
+	 * @return static
+	 */
+	public function setEndMark(string $endMark): SgmlIgnoredTag
 	{
 		$this->endMark = $endMark;
 
 		return $this;
 	}
 
-	public function getEndMark()
+	/**
+	 * @return string|null
+	 */
+	public function getEndMark(): ?string
 	{
 		return $this->endMark;
 	}
 
-	public function isComment()
+	/**
+	 * @return bool
+	 */
+	public function isComment(): bool
 	{
 		return $this->getId() == '!--';
 	}
 
-	public function isExternal()
+	/**
+	 * @return bool
+	 */
+	public function isExternal(): bool
 	{
 		return mb_substr($this->getId() ?? '', 0, 1) == '?';
 	}
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/src/Main/Markup/Html/SgmlOpenTag.php b/src/Main/Markup/Html/SgmlOpenTag.php
index 3b34ae1e3e..381fee7941 100644
--- a/src/Main/Markup/Html/SgmlOpenTag.php
+++ b/src/Main/Markup/Html/SgmlOpenTag.php
@@ -11,7 +11,6 @@
 
 namespace OnPHP\Main\Markup\Html;
 
-use OnPHP\Core\Base\Assert;
 use OnPHP\Core\Exception\WrongArgumentException;
 
 /**
@@ -19,93 +18,115 @@
 **/
 final class SgmlOpenTag extends SgmlTag
 {
-	private $attributes	= array();
-	private $empty		= false;
-
 	/**
-	 * @return SgmlOpenTag
-	**/
-	public static function create()
-	{
-		return new self;
-	}
+	 * @var array
+	 */
+	private array $attributes = [];
+	/**
+	 * @var bool
+	 */
+	private bool $empty = false;
 
 	/**
-	 * @return SgmlOpenTag
-	**/
-	public function setEmpty($isEmpty)
+	 * @param bool $isEmpty
+	 * @return static
+	 */
+	public function setEmpty(bool $isEmpty): SgmlOpenTag
 	{
-		Assert::isBoolean($isEmpty);
-
 		$this->empty = $isEmpty;
 
 		return $this;
 	}
 
-	public function isEmpty()
+	/**
+	 * @return bool
+	 */
+	public function isEmpty(): bool
 	{
 		return $this->empty;
 	}
 
 	/**
-	 * @return SgmlOpenTag
-	**/
-	public function setAttribute($name, $value)
+	 * @param string $name
+	 * @param mixed $value
+	 * @return static
+	 * @throws WrongArgumentException
+	 */
+	public function setAttribute(string $name, $value = null): SgmlOpenTag
 	{
+		if ($this->hasAttribute($name)) {
+			throw new WrongArgumentException("attribute '{$name}' already exist");
+		}
+
 		$this->attributes[$name] = $value;
 
 		return $this;
 	}
 
-	public function hasAttribute($name)
+	/**
+	 * @param string $name
+	 * @return bool
+	 */
+	public function hasAttribute(string $name): bool
 	{
-		$name = strtolower($name);
-
-		return isset($this->attributes[$name]);
+		return in_array(
+			mb_strtolower($name),
+			array_map('mb_strtolower', array_keys($this->attributes))
+		);
 	}
 
-	public function getAttribute($name)
+	/**
+	 * @param string $name
+	 * @return mixed
+	 * @throws WrongArgumentException
+	 */
+	public function getAttribute(string $name)
 	{
-		$name = strtolower($name);
+		$name = mb_strtolower($name);
 
-		if (!isset($this->attributes[$name]))
-			throw new WrongArgumentException(
-				"attribute '{$name}' does not exist"
-			);
+		foreach($this->attributes as $attributeName => $value) {
+			if (mb_strtolower($attributeName) == $name) {
+				return $value;
+			}
+		}
 
-		return $this->attributes[$name];
+		throw new WrongArgumentException("attribute '{$name}' does not exist");
 	}
 
 	/**
-	 * @return SgmlOpenTag
-	**/
-	public function dropAttribute($name)
+	 * @param string $name
+	 * @return static
+	 * @throws WrongArgumentException
+	 */
+	public function dropAttribute(string $name): SgmlOpenTag
 	{
-		$name = strtolower($name);
+		$name = mb_strtolower($name);
 
-		if (!isset($this->attributes[$name]))
-			throw new WrongArgumentException(
-				"attribute '{$name}' does not exist"
-			);
+		foreach($this->attributes as $attributeName => $value) {
+			if (mb_strtolower($attributeName) == $name) {
+				unset($this->attributes[$attributeName]);
+				return $this;
+			}
+		}
 
-		unset($this->attributes[$name]);
-
-		return $this;
+		throw new WrongArgumentException("attribute '{$name}' does not exist");
 	}
 
-	public function getAttributesList()
+	/**
+	 * @return array
+	 */
+	public function getAttributesList(): array
 	{
 		return $this->attributes;
 	}
 
 	/**
-	 * @return SgmlOpenTag
-	**/
-	public function dropAttributesList()
+	 * @return static
+	 */
+	public function dropAttributesList(): SgmlOpenTag
 	{
 		$this->attributes = array();
 
 		return $this;
 	}
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/src/Main/Markup/Html/SgmlTag.php b/src/Main/Markup/Html/SgmlTag.php
index 5988b48705..f8327287e2 100644
--- a/src/Main/Markup/Html/SgmlTag.php
+++ b/src/Main/Markup/Html/SgmlTag.php
@@ -17,21 +17,27 @@
 **/
 abstract class SgmlTag extends SgmlToken
 {
-	private $id = null;
+	/**
+	 * @var string|null
+	 */
+	private ?string $id = null;
 
 	/**
-	 * @return SgmlTag
-	**/
-	public function setId($id)
+	 * @param string|null $id
+	 * @return static
+	 */
+	public function setId(?string $id): SgmlTag
 	{
 		$this->id = $id;
 
 		return $this;
 	}
 
-	public function getId()
+	/**
+	 * @return string|null
+	 */
+	public function getId(): ?string
 	{
 		return $this->id;
 	}
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/src/Main/Markup/Html/SgmlToken.php b/src/Main/Markup/Html/SgmlToken.php
index 901cad2b92..6af024f182 100644
--- a/src/Main/Markup/Html/SgmlToken.php
+++ b/src/Main/Markup/Html/SgmlToken.php
@@ -17,21 +17,35 @@
 **/
 class SgmlToken
 {
-	private $value	= null;
+	/**
+	 * @var string|null
+	 */
+	private ?string $value	= null;
+
+	/**
+	 * @return static
+	 */
+	public static function create(): SgmlToken
+	{
+		return new static;
+	}
 
 	/**
-	 * @return SgmlToken
-	**/
-	public function setValue($value)
+	 * @param string|null $value
+	 * @return static
+	 */
+	public function setValue(?string $value): SgmlToken
 	{
 		$this->value = $value;
 
 		return $this;
 	}
 
-	public function getValue()
+	/**
+	 * @return string|null
+	 */
+	public function getValue(): ?string
 	{
 		return $this->value;
 	}
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/src/Main/Message/Specification/MessageQueue.php b/src/Main/Message/Specification/MessageQueue.php
index 6e0d8ecb1f..c3fc3658dc 100644
--- a/src/Main/Message/Specification/MessageQueue.php
+++ b/src/Main/Message/Specification/MessageQueue.php
@@ -11,6 +11,4 @@
 
 namespace OnPHP\Main\Message\Specification;
 
-interface MessageQueue { /* nop */ }
-
-?>
\ No newline at end of file
+interface MessageQueue { /* nop */ }
\ No newline at end of file
diff --git a/src/Main/Message/Specification/MessageQueueReceiver.php b/src/Main/Message/Specification/MessageQueueReceiver.php
index 88eb7d0ae2..e2489f6fcd 100644
--- a/src/Main/Message/Specification/MessageQueueReceiver.php
+++ b/src/Main/Message/Specification/MessageQueueReceiver.php
@@ -16,11 +16,10 @@ interface MessageQueueReceiver
 	/**
 	 * @return Message
 	**/
-	public function receive($uTimeout = null);
+	public function receive(int $uTimeout = null);
 
 	/**
 	 * @return MessageQueue
 	**/
 	public function getQueue();
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/src/Main/Message/TextFileQueue.php b/src/Main/Message/TextFileQueue.php
index fde6ee412e..75605098dd 100644
--- a/src/Main/Message/TextFileQueue.php
+++ b/src/Main/Message/TextFileQueue.php
@@ -15,36 +15,58 @@
 
 class TextFileQueue implements MessageQueue
 {
-	private $fileName	= null;
-	private $offset		= null;
+	/**
+	 * @var string|null
+	 */
+	private ?string $fileName = null;
+	/**
+	 * @var int|null
+	 */
+	private ?int $offset = 0;
 
-	public static function create()
+	/**
+	 * @return static
+	 */
+	public static function create(): TextFileQueue
 	{
-		return new self;
+		return new static;
 	}
 
-	public function setFileName($fileName)
+	/**
+	 * @param string $fileName
+	 * @return static
+	 */
+	public function setFileName(?string $fileName): TextFileQueue
 	{
 		$this->fileName = $fileName;
 
 		return $this;
 	}
 
-	public function getFileName()
+	/**
+	 * @return string|null
+	 */
+	public function getFileName(): ?string
 	{
 		return $this->fileName;
 	}
 
-	public function setOffset($offset)
+	/**
+	 * @param int $offset
+	 * @return static
+	 */
+	public function setOffset(int $offset): TextFileQueue
 	{
 		$this->offset = $offset;
 
 		return $this;
 	}
 
-	public function getOffset()
+	/**
+	 * @return int
+	 */
+	public function getOffset(): int
 	{
 		return $this->offset;
 	}
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/src/Main/Message/TextFileReceiver.php b/src/Main/Message/TextFileReceiver.php
index f93dda818d..0868e18b96 100644
--- a/src/Main/Message/TextFileReceiver.php
+++ b/src/Main/Message/TextFileReceiver.php
@@ -13,29 +13,34 @@
 
 use OnPHP\Core\Base\Assert;
 use OnPHP\Core\Base\Timestamp;
+use OnPHP\Core\Exception\IOException;
+use OnPHP\Core\Exception\WrongArgumentException;
 use OnPHP\Core\Exception\WrongStateException;
 use OnPHP\Main\Message\Specification\Message;
 use OnPHP\Main\Message\Specification\MessageQueue;
 use OnPHP\Main\Message\Specification\MessageQueueReceiver;
 use OnPHP\Main\Util\IO\FileInputStream;
+use OnPHP\Main\Util\IO\InputStream;
 
 final class TextFileReceiver implements MessageQueueReceiver
 {
-	private $queue	= null;
-	private $stream	= null;
+	private ?MessageQueue $queue = null;
+	private ?FileInputStream $stream = null;
 
 	/**
-	 * @return TextFileReceiver
-	**/
-	public static function create()
+	 * @return static
+	 */
+	public static function create(): TextFileReceiver
 	{
 		return new self;
 	}
 
 	/**
-	 * @return TextFileReceiver
-	**/
-	public function setQueue(MessageQueue $queue)
+	 * @param MessageQueue $queue
+	 * @return static
+	 * @throws WrongArgumentException
+	 */
+	public function setQueue(MessageQueue $queue): TextFileReceiver
 	{
 		Assert::isInstance($queue, TextFileQueue::class);
 
@@ -45,61 +50,70 @@ public function setQueue(MessageQueue $queue)
 	}
 
 	/**
-	 * @return MessageQueue
-	**/
-	public function getQueue()
+	 * @return MessageQueue|null
+	 */
+	public function getQueue(): ?MessageQueue
 	{
 		return $this->queue;
 	}
 
 	/**
-	 * @return Message
-	**/
-	public function receive($uTimeout = null)
+	 * @param int|null $uTimeout
+	 * @return Message|null
+	 * @throws WrongArgumentException
+	 * @throws WrongStateException
+	 * @throws IOException
+	 */
+	public function receive(int $uTimeout = null): ?Message
 	{
-		if (!$this->queue)
+		if (!$this->queue instanceof MessageQueue) {
 			throw new WrongStateException('you must set the queue first');
+		}
 
-		if ($uTimeout && $this->getStream()->isEof())
+		if ($uTimeout && $this->getStream()->isEof()) {
 			usleep($uTimeout);
+		}
 
 		$string = $this->getStream()->readString();
 
-		if (!$string && $this->getStream()->isEof())
+		if (!$string && $this->getStream()->isEof()) {
 			return null;
+		}
 
-		$this->getQueue()->setOffset($this->getStream()->getOffset());
+		if (($streamOffset = $this->getStream()->getOffset()) !== false) {
+			$this->getQueue()->setOffset($streamOffset);
+		}
 
 		$string = rtrim($string, PHP_EOL);
-
 		$chunks = preg_split("/\t/", $string, 2);
 
-		$time = isset($chunks[0]) ? $chunks[0] : null;
-		$text = isset($chunks[1]) ? $chunks[1] : null;
+		$time = $chunks[0] ?? null;
+		$text = $chunks[1] ?? null;
 
 		Assert::isNotNull($time);
 
-		$result = TextMessage::create(Timestamp::create($time))->
-			setText($text);
+		$result = TextMessage::create(Timestamp::create($time))
+			->setText($text);
 
 		return $result;
 	}
 
 	/**
-	 * @return FileInputStream
-	**/
-	private function getStream()
+	 * @return FileInputStream|null
+	 * @throws IOException
+	 * @throws WrongArgumentException
+	 */
+	private function getStream(): ?FileInputStream
 	{
-		if (!$this->stream) {
+		if (!$this->stream instanceof InputStream) {
 			Assert::isNotNull($this->queue->getFileName());
 
-			$this->stream = FileInputStream::create(
-				$this->queue->getFileName()
-			)->
-				seek($this->queue->getOffset());
+			$this->stream =
+				FileInputStream::create(
+					$this->queue->getFileName()
+				)->seek($this->queue->getOffset());
 		}
 
 		return $this->stream;
 	}
-}
-?>
+}
\ No newline at end of file
diff --git a/src/Main/Util/IO/BufferedInputStream.php b/src/Main/Util/IO/BufferedInputStream.php
index 115db6698f..d9d5a9ebfe 100644
--- a/src/Main/Util/IO/BufferedInputStream.php
+++ b/src/Main/Util/IO/BufferedInputStream.php
@@ -16,10 +16,10 @@
 **/
 final class BufferedInputStream extends InputStream
 {
-	private $runAheadBytes	= 0;
+	private int $runAheadBytes = 0;
 
-	private $in				= null;
-	private $closed			= false;
+	private InputStream $in;
+	private bool $closed = false;
 
 	private $buffer			= null;
 	private $bufferLength	= 0;
@@ -33,37 +33,44 @@ public function __construct(InputStream $in)
 	}
 
 	/**
-	 * @return BufferedInputStream
-	**/
-	public static function create(InputStream $in)
+	 * @param InputStream $in
+	 * @return static
+	 */
+	public static function create(InputStream $in): BufferedInputStream
 	{
 		return new self($in);
 	}
 
 	/**
-	 * @return BufferedInputStream
-	**/
-	public function close()
+	 * @return static
+	 */
+	public function close(): BufferedInputStream
 	{
 		$this->closed = true;
 
 		return $this;
 	}
 
-	public function isEof()
+	/**
+	 * @return bool
+	 */
+	public function isEof(): bool
 	{
 		return $this->in->isEof();
 	}
 
-	public function markSupported()
+	/**
+	 * @return bool
+	 */
+	public function markSupported(): bool
 	{
 		return true;
 	}
 
 	/**
-	 * @return BufferedInputStream
-	**/
-	public function mark()
+	 * @return static
+	 */
+	public function mark(): BufferedInputStream
 	{
 		$this->markPosition = $this->position;
 
@@ -71,43 +78,52 @@ public function mark()
 	}
 
 	/**
-	 * @return BufferedInputStream
-	**/
-	public function reset()
+	 * @return static
+	 */
+	public function reset(): BufferedInputStream
 	{
 		$this->position = $this->markPosition;
 
 		return $this;
 	}
 
-	public function available()
+	/**
+	 * @return int
+	 */
+	public function available(): int
 	{
-		if ($this->closed)
+		if ($this->closed) {
 			return 0;
+		}
 
 		return ($this->bufferLength - $this->position);
 	}
 
 	/**
-	 * @return BufferedInputStream
-	**/
-	public function setRunAheadBytes($runAheadBytes)
+	 * @param int $runAheadBytes
+	 * @return static
+	 */
+	public function setRunAheadBytes(int $runAheadBytes): BufferedInputStream
 	{
 		$this->runAheadBytes = $runAheadBytes;
 
 		return $this;
 	}
 
-	public function read($count)
+	/**
+	 * @param int $length
+	 * @return string|null
+	 */
+	public function read(int $length): ?string
 	{
 		if ($this->closed)
 			return null;
 
-		$remainingCount = $count;
+		$remainingCount = $length;
 		$availableCount = $this->available();
 
 		if ($remainingCount <= $availableCount)
-			$readFromBuffer = $count;
+			$readFromBuffer = $length;
 		else
 			$readFromBuffer = $availableCount;
 
@@ -147,5 +163,4 @@ public function read($count)
 
 		return $result;
 	}
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/src/Main/Util/IO/FileInputStream.php b/src/Main/Util/IO/FileInputStream.php
index 5a65c971aa..df8a733011 100644
--- a/src/Main/Util/IO/FileInputStream.php
+++ b/src/Main/Util/IO/FileInputStream.php
@@ -19,18 +19,24 @@
 **/
 final class FileInputStream extends InputStream
 {
-	private $fd		= null;
-
-	private $mark	= null;
+	/**
+	 * @var resource
+	 */
+	private $fd;
+	private $mark = null;
 
+	/**
+	 * @param resource $nameOrFd
+	 * @throws IOException
+	 */
 	public function __construct($nameOrFd)
 	{
 		if (is_resource($nameOrFd)) {
-			if (get_resource_type($nameOrFd) !== 'stream')
+			if (get_resource_type($nameOrFd) !== 'stream') {
 				throw new IOException('not a file resource');
+			}
 
 			$this->fd = $nameOrFd;
-
 		} else {
 			try {
 				$this->fd = fopen($nameOrFd, 'rb');
@@ -50,81 +56,112 @@ public function __destruct()
 	}
 
 	/**
-	 * @return FileInputStream
-	**/
-	public static function create($nameOrFd)
+	 * @param resource $nameOrFd
+	 * @return static
+	 * @throws IOException
+	 */
+	public static function create($nameOrFd): FileInputStream
 	{
 		return new self($nameOrFd);
 	}
 
-	public function isEof()
+	/**
+	 * @return bool
+	 */
+	public function isEof(): bool
 	{
 		return feof($this->fd);
 	}
 
 	/**
-	 * @return FileInputStream
-	**/
-	public function mark()
+	 * @return static
+	 */
+	public function mark(): FileInputStream
 	{
 		$this->mark = $this->getOffset();
 
 		return $this;
 	}
 
+	/**
+	 * @return false|int
+	 */
 	public function getOffset()
 	{
 		return ftell($this->fd);
 	}
 
-	public function markSupported()
+	/**
+	 * @return bool
+	 */
+	public function markSupported(): bool
 	{
 		return true;
 	}
 
 	/**
-	 * @return FileInputStream
-	**/
-	public function reset()
+	 * @return static
+	 * @throws IOException
+	 */
+	public function reset(): FileInputStream
 	{
 		return $this->seek($this->mark);
 	}
 
 	/**
-	 * @return FileInputStream
-	**/
-	public function seek($offset)
+	 * @param int $offset
+	 * @return static
+	 * @throws IOException
+	 */
+	public function seek(int $offset): FileInputStream
 	{
-		if (fseek($this->fd, $offset) < 0)
-			throw new IOException(
-				'mark has been invalidated'
-			);
+		if (fseek($this->fd, $offset) < 0) {
+			throw new IOException('mark has been invalidated');
+		}
 
 		return $this;
 	}
 
 	/**
-	 * @return FileInputStream
-	**/
-	public function close()
+	 * @return static
+	 * @throws IOException
+	 */
+	public function close(): FileInputStream
 	{
-		if (!fclose($this->fd))
+		if (!fclose($this->fd)) {
 			throw new IOException('failed to close the file');
+		}
 
 		return $this;
 	}
 
-	public function read($length)
+	/**
+	 * @param int $length
+	 * @return string|null
+	 * @throws IOException
+	 */
+	public function read(int $length): ?string
 	{
 		return $this->realRead($length);
 	}
 
-	public function readString($length = null)
+	/**
+	 * @param int|null $length
+	 * @return string|null
+	 * @throws IOException
+	 */
+	public function readString(int $length = null): ?string
 	{
 		return $this->realRead($length, true);
 	}
 
-	public function realRead($length, $string = false)
+	/**
+	 * @param int $length
+	 * @param bool $string
+	 * @return string|null
+	 * @throws IOException
+	 */
+	public function realRead(int $length = null, bool $string = false): ?string
 	{
 		$result = $string
 			? (
@@ -134,16 +171,18 @@ public function realRead($length, $string = false)
 			)
 			: fread($this->fd, $length);
 
-		if ($string && $result === false && feof($this->fd))
+		if ($string && $result === false && feof($this->fd)) {
 			$result = null; // fgets returns false on eof
+		}
 
-		if ($result === false)
+		if ($result === false) {
 			throw new IOException('failed to read from file');
+		}
 
-		if ($result === '')
+		if ($result === '') {
 			$result = null; // eof
+		}
 
 		return $result;
 	}
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/src/Main/Util/IO/InputStream.php b/src/Main/Util/IO/InputStream.php
index c31fa3566c..e0b451abad 100644
--- a/src/Main/Util/IO/InputStream.php
+++ b/src/Main/Util/IO/InputStream.php
@@ -31,51 +31,70 @@ abstract class InputStream
 	 * 
 	 * It is abnormal state. Maybe you should use some kind of
 	 * non-blocking channels instead?
-	 * 
-	**/
-	abstract public function read($length);
-	abstract public function isEof();
+	 *
+	 * @param int $length
+	 * @return string|null
+	 */
+	abstract public function read(int $length): ?string;
+
+	/**
+	 * @return bool
+	 */
+	abstract public function isEof(): bool;
 
 	/**
-	 * @return InputStream
-	**/
-	public function mark()
+	 * @return static
+	 */
+	public function mark(): InputStream
 	{
 		/* nop */
 
 		return $this;
 	}
 
-	public function markSupported()
+	/**
+	 * @return bool
+	 */
+	public function markSupported(): bool
 	{
 		return false;
 	}
 
-	public function reset()
+	/**
+	 * @return static
+	 * @throws IOException
+	 */
+	public function reset(): InputStream
 	{
 		throw new IOException(
 			'mark has been invalidated'
 		);
 	}
 
-	public function skip($count)
+	/**
+	 * @param int $count
+	 * @return int
+	 */
+	public function skip(int $count): int
 	{
-		return strlen($this->read($count));
+		return mb_strlen($this->read($count));
 	}
 
-	public function available()
+	/**
+	 * @return int
+	 */
+	public function available(): int
 	{
 		return 0;
 	}
 
 	/**
-	 * @return InputStream
-	**/
-	public function close()
+	 * @return static
+	 */
+	public function close(): InputStream
 	{
 		/* nop */
 
 		return $this;
 	}
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/src/Main/Util/IO/SocketInputStream.php b/src/Main/Util/IO/SocketInputStream.php
index d624c847ad..d2aebaa144 100644
--- a/src/Main/Util/IO/SocketInputStream.php
+++ b/src/Main/Util/IO/SocketInputStream.php
@@ -30,20 +30,31 @@ final class SocketInputStream extends InputStream
 	**/
 	const READ_ATTEMPTS = 15; // should be enough for everyone (C)
 
-	private $socket	= null;
-	private $eof	= false;
+	private Socket $socket;
+	private bool $eof = false;
 
+	/**
+	 * @param Socket $socket
+	 */
 	public function __construct(Socket $socket)
 	{
 		$this->socket = $socket;
 	}
 
-	public function isEof()
+	/**
+	 * @return bool
+	 */
+	public function isEof(): bool
 	{
 		return $this->eof;
 	}
 
-	public function read($length)
+	/**
+	 * @param int $length
+	 * @return string|null
+	 * @throws IOException
+	 */
+	public function read(int $length): ?string
 	{
 		if ($length == 0 || $this->eof)
 			return null;
@@ -87,5 +98,4 @@ public function read($length)
 
 		return $result;
 	}
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/src/Main/Util/IO/StringInputStream.php b/src/Main/Util/IO/StringInputStream.php
index bc9922a5d4..9cc26a6441 100644
--- a/src/Main/Util/IO/StringInputStream.php
+++ b/src/Main/Util/IO/StringInputStream.php
@@ -18,52 +18,60 @@
 **/
 final class StringInputStream extends InputStream
 {
-	private $string		= null;
-	private $length		= null;
+	private string $string;
+	private ?int $length    = null;
 
-	private $position	= 0;
-	private $mark		= 0;
+	private int $position	= 0;
+	private int $mark		= 0;
 
-	public function __construct($string)
+	/**
+	 * @param string $string
+	 */
+	public function __construct(string $string)
 	{
-		Assert::isString($string);
-
 		$this->string = $string;
 		$this->length = strlen($string);
 	}
 
 	/**
-	 * @return StringInputStream
-	**/
-	public static function create($string)
+	 * @param string $string
+	 * @return self
+	 */
+	public static function create(string $string): StringInputStream
 	{
 		return new self($string);
 	}
 
-	public function isEof()
+	/**
+	 * @return bool
+	 */
+	public function isEof(): bool
 	{
 		return ($this->position >= $this->length);
 	}
 
 	/**
-	 * @return StringInputStream
-	**/
-	public function mark()
+	 * @return static
+	 */
+	public function mark(): StringInputStream
 	{
 		$this->mark = $this->position;
 
 		return $this;
 	}
 
-	public function markSupported()
+	/**
+	 * @return bool
+	 */
+	public function markSupported():bool
 	{
 		return true;
 	}
 
 	/**
-	 * @return StringInputStream
-	**/
-	public function reset()
+	 * @return static
+	 */
+	public function reset(): StringInputStream
 	{
 		$this->position = $this->mark;
 
@@ -71,16 +79,20 @@ public function reset()
 	}
 
 	/**
-	 * @return StringInputStream
-	**/
-	public function close()
+	 * @return static
+	 */
+	public function close(): StringInputStream
 	{
 		$this->string = null;
 
 		return $this;
 	}
 
-	public function read($count)
+	/**
+	 * @param int $count
+	 * @return string|null
+	 */
+	public function read(int $count): ?string
 	{
 		if (!$this->string || $this->isEof())
 			return null;
@@ -88,12 +100,11 @@ public function read($count)
 		if ($count == 1) {
 			$result = $this->string[(int)$this->position];
 		} else {
-			$result = substr($this->string, $this->position, $count);
+			$result = mb_substr($this->string, $this->position, $count);
 		}
 
 		$this->position += $count;
 
 		return $result;
 	}
-}
-?>
\ No newline at end of file
+}
\ No newline at end of file
diff --git a/tests/Main/Markup/CdataTest.php b/tests/Main/Markup/CdataTest.php
new file mode 100644
index 0000000000..c3bbf89c26
--- /dev/null
+++ b/tests/Main/Markup/CdataTest.php
@@ -0,0 +1,51 @@
+<?php
+/***************************************************************************
+ *   Copyright (C) 2021 by Sergei V. Deriabin                              *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License as        *
+ *   published by the Free Software Foundation; either version 3 of the    *
+ *   License, or (at your option) any later version.                       *
+ *                                                                         *
+ ***************************************************************************/
+
+namespace OnPHP\Tests\Main\Markup;
+
+use OnPHP\Main\Markup\Html\Cdata;
+use OnPHP\Tests\TestEnvironment\TestCase;
+
+class CdataTest extends TestCase
+{
+	public function testCreate()
+	{
+		$tag = Cdata::create();
+		$this->assertInstanceOf(Cdata::class, $tag);
+	}
+
+	public function testStrict()
+	{
+		$tag = Cdata::create();
+		$this->assertFalse($tag->isStrict());
+
+		$this->assertInstanceOf(Cdata::class, $tag->setStrict(true));
+		$this->assertTrue($tag->isStrict());
+	}
+
+	public function testData()
+	{
+		$tag = Cdata::create();
+		$this->assertNull($tag->getData());
+		$this->assertNull($tag->getRawData());
+
+		$data = 'test data content';
+		$tag->setData($data);
+		$this->assertEquals($data, $tag->getRawData());
+		$this->assertEquals($data, $tag->getData());
+		$tag->setStrict(true);
+		$this->assertEquals($data, $tag->getRawData());
+		$this->assertEquals(
+			Cdata::CDATA_STRICT_START . $data . Cdata::CDATA_STRICT_END,
+			$tag->getData()
+		);
+	}
+}
\ No newline at end of file
diff --git a/tests/Main/Markup/HtmlAssemblerTest.php b/tests/Main/Markup/HtmlAssemblerTest.php
new file mode 100644
index 0000000000..d8336bb47a
--- /dev/null
+++ b/tests/Main/Markup/HtmlAssemblerTest.php
@@ -0,0 +1,335 @@
+<?php
+/***************************************************************************
+ *   Copyright (C) 2021 by Sergei V. Deriabin                              *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License as        *
+ *   published by the Free Software Foundation; either version 3 of the    *
+ *   License, or (at your option) any later version.                       *
+ *                                                                         *
+ ***************************************************************************/
+
+namespace OnPHP\Tests\Main\Markup;
+
+use OnPHP\Core\Exception\UnimplementedFeatureException;
+use OnPHP\Core\Exception\WrongArgumentException;
+use OnPHP\Main\Markup\Html\Cdata;
+use OnPHP\Main\Markup\Html\HtmlAssembler;
+use OnPHP\Main\Markup\Html\HtmlTokenizer;
+use OnPHP\Main\Markup\Html\SgmlEndTag;
+use OnPHP\Main\Markup\Html\SgmlIgnoredTag;
+use OnPHP\Main\Markup\Html\SgmlOpenTag;
+use OnPHP\Main\Util\IO\StringInputStream;
+use OnPHP\Tests\TestEnvironment\SgmlTag;
+use OnPHP\Tests\TestEnvironment\TestCase;
+
+class HtmlAssemblerTest extends TestCase
+{
+	public function testConstructor()
+	{
+		$html = new HtmlAssembler([]);
+		$this->assertNull($html->getHtml());
+		$this->assertEmpty($this->getObjectProperty($html, 'tags'));
+
+		$input = [
+			SgmlOpenTag::create()->setId('div'),
+			Cdata::create()->setData('test text'),
+			SgmlEndTag::create()->setId('div')
+		];
+		$html = new HtmlAssembler($input);
+		$tags = $this->getObjectProperty($html, 'tags');
+		$this->assertCount(3, $tags);
+		$this->assertEquals($input, $tags);
+
+		$input[] = 'test string';
+		$this->expectException(WrongArgumentException::class);
+		new HtmlAssembler($input);
+	}
+
+	public function testMakeTag()
+	{
+		$cdata = Cdata::create()->setData('test-data');
+		$this->assertEquals($cdata->getData(), HtmlAssembler::makeTag($cdata));
+		$cdata->setStrict(true);
+		$this->assertEquals($cdata->getData(), HtmlAssembler::makeTag($cdata));
+
+		try {
+			HtmlAssembler::makeTag(SgmlIgnoredTag::create());
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$this->assertEquals(
+			'<!---->',
+			HtmlAssembler::makeTag(SgmlIgnoredTag::comment())
+		);
+		$this->assertEquals(
+			'<!--comment-->',
+			HtmlAssembler::makeTag(
+				SgmlIgnoredTag::comment()->setCdata(Cdata::create()->setData('comment'))
+			)
+		);
+		$cdata = Cdata::create()->setData('comment')->setStrict(true);
+		$this->assertEquals(
+			'<!--'.$cdata->getData().'-->',
+			HtmlAssembler::makeTag(
+				SgmlIgnoredTag::comment()->setCdata($cdata)
+			)
+		);
+		$cdata = Cdata::create()->setData(' /* PHP code */ ');
+		$this->assertEquals(
+			'<?php'.$cdata->getData().'?>',
+			HtmlAssembler::makeTag(
+				SgmlIgnoredTag::create()->setId('?php')->setEndMark('?')->setCdata($cdata)
+			)
+		);
+
+		try {
+			HtmlAssembler::makeTag(SgmlOpenTag::create());
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$this->assertEquals(
+			'<div>',
+			HtmlAssembler::makeTag(SgmlOpenTag::create()->setId('div'))
+		);
+		$this->assertEquals(
+			'<div/>',
+			HtmlAssembler::makeTag(SgmlOpenTag::create()->setId('div')->setEmpty(true))
+		);
+		$this->assertEquals(
+			'<div class="test"/>',
+			HtmlAssembler::makeTag(
+				SgmlOpenTag::create()->setId('div')->setEmpty(true)->setAttribute('class', 'test')
+			)
+		);
+		$this->assertEquals(
+			'<div class="test" required/>',
+			HtmlAssembler::makeTag(
+				SgmlOpenTag::create()
+					->setId('div')->setEmpty(true)
+					->setAttribute('class', 'test')
+					->setAttribute('required')
+			)
+		);
+
+		try {
+			HtmlAssembler::makeTag(SgmlEndTag::create());
+			$this->fail('expected WrongArgumentException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$this->assertEquals(
+			'</div>',
+			HtmlAssembler::makeTag(SgmlEndTag::create()->setId('div'))
+		);
+
+		$this->expectException(WrongArgumentException::class);
+		HtmlAssembler::makeTag(SgmlTag::create());
+	}
+
+	public function testMakeDomNode()
+	{
+		$doc = new \DOMDocument("1.0");
+
+		try {
+			HtmlAssembler::makeDomNode($doc);
+			$this->fail('expected UnimplementedFeatureException exception');
+		} catch(\Throwable $exception) {
+			$this->assertInstanceOf(UnimplementedFeatureException::class, $exception);
+		}
+
+		$node = $doc->appendChild($doc->createElement("div"));
+		$this->assertEquals('<div />', HtmlAssembler::makeDomNode($node));
+
+		$node->setAttribute("data-test", null);
+		$this->assertEquals('<div data-test />', HtmlAssembler::makeDomNode($node));
+		$node->setAttribute('class', 'test');
+		$this->assertEquals('<div data-test class="test" />', HtmlAssembler::makeDomNode($node));
+
+		$node->appendChild($doc->createTextNode("test content"));
+		$this->assertEquals(
+			'<div data-test class="test">test content</div>',
+			HtmlAssembler::makeDomNode($node)
+		);
+
+		$em = $doc->createElement("em");
+		$em->appendChild($doc->createTextNode('test em'));
+		$node->appendChild($em);
+		$node->appendChild($doc->createTextNode("appendix"));
+		$this->assertEquals(
+			'<div data-test class="test">test content'
+				. '<em>test em</em>appendix</div>',
+			HtmlAssembler::makeDomNode($node)
+		);
+
+		$node->appendChild($doc->createElement("img"));
+		$this->assertEquals(
+			'<div data-test class="test">test content'
+			. '<em>test em</em>appendix<img /></div>',
+			HtmlAssembler::makeDomNode($node)
+		);
+	}
+
+	public function testGetAttributes()
+	{
+		$this->assertEmpty(
+			$this->callObjectMethod(
+				HtmlAssembler::class,
+				'getAttributes',
+				SgmlOpenTag::create()->setId('div')
+			)
+		);
+
+		$this->assertEquals(
+			'data-test',
+			$this->callObjectMethod(
+				HtmlAssembler::class,
+				'getAttributes',
+				SgmlOpenTag::create()->setId('div')->setAttribute('data-test')
+			)
+		);
+
+		$this->assertEquals(
+			'class="test"',
+			$this->callObjectMethod(
+				HtmlAssembler::class,
+				'getAttributes',
+				SgmlOpenTag::create()->setId('div')->setAttribute('class', 'test')
+			)
+		);
+
+		$this->assertEquals(
+			'class="test" data-test',
+			$this->callObjectMethod(
+				HtmlAssembler::class,
+				'getAttributes',
+				SgmlOpenTag::create()->setId('div')
+					->setAttribute('class', 'test')
+					->setAttribute('data-test')
+			)
+		);
+
+		$this->assertEquals(
+			'class="test" data-test id="&quot;id"',
+			$this->callObjectMethod(
+				HtmlAssembler::class,
+				'getAttributes',
+				SgmlOpenTag::create()->setId('div')
+					->setAttribute('class', 'test')
+					->setAttribute('data-test')
+					->setAttribute('id', '"id')
+			)
+		);
+	}
+
+	public function testGetDomAttributes()
+	{
+		$doc = new \DOMDocument("1.0");
+		$node = $doc->appendChild($doc->createElement("div"));
+
+		$this->assertEmpty(
+			$this->callObjectMethod(
+				HtmlAssembler::class,
+				'getDomAttributes',
+				$node
+			)
+		);
+
+		$node->setAttribute("data-test", null);
+		$this->assertEquals(
+			'data-test',
+			$this->callObjectMethod(
+				HtmlAssembler::class,
+				'getDomAttributes',
+				$node
+			)
+		);
+
+		$node->setAttribute('class', 'test');
+		$this->assertEquals(
+			'data-test class="test"',
+			$this->callObjectMethod(
+				HtmlAssembler::class,
+				'getDomAttributes',
+				$node
+			)
+		);
+
+		$node->setAttribute('id', '"id');
+		$this->assertEquals(
+			'data-test class="test" id="&quot;id"',
+			$this->callObjectMethod(
+				HtmlAssembler::class,
+				'getDomAttributes',
+				$node
+			)
+		);
+	}
+
+	public function testReadAndBuid()
+	{
+		$html = <<<HTML
+<!doctype html>
+<html dir="ltr" lang="ru">
+  <head>
+    <meta charset="utf-8">
+    <title>Новая вкладка</title>
+    <style>
+      body {
+        background: #FFFFFF;
+        margin: 0;
+      }
+
+      #oneGoogleBar {
+        height: 56px;
+      }
+
+      #backgroundImage {
+        border: none;
+        height: 100%;
+        pointer-events: none;
+        position: fixed;
+        top: 0;
+        visibility: hidden;
+        width: 100%;
+      }
+
+      [show-background-image] #backgroundImage {
+        visibility: visible;
+      }
+    </style>
+  </head>
+  <body>
+    <div id="oneGoogleBar"></div>
+    <iframe id="backgroundImage"
+        src="chrome-untrusted://new-tab-page/custom_background_image?url=">
+    </iframe>
+    <ntp-app></ntp-app>
+    <script type="module" src="new_tab_page.js"></script>
+    <link rel="stylesheet" href="chrome://resources/css/text_defaults_md.css">
+    <link rel="stylesheet" href="shared_vars.css">
+    <div id="oneGoogleBarEndOfBody"></div>
+  </body>
+</html>
+HTML;
+		$tags = [];
+		$reader = HtmlTokenizer::create(StringInputStream::create($html));
+		while(($tag = $reader->nextToken()) !== null) {
+			$tags[] = $tag;
+		}
+		$html = (new HtmlAssembler($tags))->getHtml();
+		/**
+		 * Need one iteration, because original rules of quotes and
+		 * writing tags may difference
+		 */
+		$tags = [];
+		$reader = HtmlTokenizer::create(StringInputStream::create($html));
+		while(($tag = $reader->nextToken()) !== null) {
+			$tags[] = $tag;
+		}
+
+		$this->assertEquals($html, (new HtmlAssembler($tags))->getHtml());
+	}
+}
\ No newline at end of file
diff --git a/tests/Main/Markup/SgmlEndTagTest.php b/tests/Main/Markup/SgmlEndTagTest.php
new file mode 100644
index 0000000000..72b939aeea
--- /dev/null
+++ b/tests/Main/Markup/SgmlEndTagTest.php
@@ -0,0 +1,24 @@
+<?php
+/***************************************************************************
+ *   Copyright (C) 2021 by Sergei V. Deriabin                              *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License as        *
+ *   published by the Free Software Foundation; either version 3 of the    *
+ *   License, or (at your option) any later version.                       *
+ *                                                                         *
+ ***************************************************************************/
+
+namespace OnPHP\Tests\Main\Markup;
+
+use OnPHP\Main\Markup\Html\SgmlEndTag;
+use OnPHP\Tests\TestEnvironment\TestCase;
+
+class SgmlEndTagTest extends TestCase
+{
+	public function testCreate()
+	{
+		$tag = SgmlEndTag::create();
+		$this->assertInstanceOf(SgmlEndTag::class, $tag);
+	}
+}
\ No newline at end of file
diff --git a/tests/Main/Markup/SgmlIgnoredTagTest.php b/tests/Main/Markup/SgmlIgnoredTagTest.php
new file mode 100644
index 0000000000..6e4eb4dcf9
--- /dev/null
+++ b/tests/Main/Markup/SgmlIgnoredTagTest.php
@@ -0,0 +1,72 @@
+<?php
+/***************************************************************************
+ *   Copyright (C) 2021 by Sergei V. Deriabin                              *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License as        *
+ *   published by the Free Software Foundation; either version 3 of the    *
+ *   License, or (at your option) any later version.                       *
+ *                                                                         *
+ ***************************************************************************/
+
+namespace OnPHP\Tests\Main\Markup;
+
+use OnPHP\Main\Markup\Html\Cdata;
+use OnPHP\Main\Markup\Html\SgmlIgnoredTag;
+use OnPHP\Tests\TestEnvironment\TestCase;
+
+class SgmlIgnoredTagTest extends TestCase
+{
+	public function testCreate()
+	{
+		$this->assertInstanceOf(SgmlIgnoredTag::class, SgmlIgnoredTag::create());
+	}
+
+	public function testComment()
+	{
+		$tag = SgmlIgnoredTag::comment();
+
+		$this->assertInstanceOf(SgmlIgnoredTag::class, $tag);
+		$this->assertEquals('!--', $tag->getId());
+		$this->assertEquals('--', $tag->getEndMark());
+		$this->assertTrue($tag->isComment());
+		$tag->setId('!-');
+		$this->assertFalse($tag->isComment());
+	}
+
+	public function testCData()
+	{
+		$tag = SgmlIgnoredTag::comment();
+
+		$this->assertNull($tag->getCdata());
+		$tag->setCdata((new Cdata())->setData('test data'));
+		$this->assertInstanceOf(Cdata::class, $tag->getCdata());
+		$this->assertEquals('test data', $tag->getCdata()->getData());
+	}
+
+	public function testEndMark()
+	{
+		$tag = SgmlIgnoredTag::create();
+
+		$this->assertNull($tag->getEndMark());
+		$tag->setEndMark('test-end-mark');
+		$this->assertEquals('test-end-mark', $tag->getEndMark());
+		$tag->setEndMark('');
+		$this->assertEquals('', $tag->getEndMark());
+	}
+
+	public function testExternal()
+	{
+		$tag = SgmlIgnoredTag::create();
+
+		$this->assertFalse($tag->isExternal());
+		$tag->setId('!--');
+		$this->assertFalse($tag->isExternal());
+		$tag->setId('?id');
+		$this->assertTrue($tag->isExternal());
+		$tag->setId('?');
+		$this->assertTrue($tag->isExternal());
+		$tag->setId('');
+		$this->assertFalse($tag->isExternal());
+	}
+}
\ No newline at end of file
diff --git a/tests/Main/Markup/SgmlOpenTagTest.php b/tests/Main/Markup/SgmlOpenTagTest.php
new file mode 100644
index 0000000000..a4e7eca42c
--- /dev/null
+++ b/tests/Main/Markup/SgmlOpenTagTest.php
@@ -0,0 +1,121 @@
+<?php
+/***************************************************************************
+ *   Copyright (C) 2021 by Sergei V. Deriabin                              *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License as        *
+ *   published by the Free Software Foundation; either version 3 of the    *
+ *   License, or (at your option) any later version.                       *
+ *                                                                         *
+ ***************************************************************************/
+
+namespace OnPHP\Tests\Main\Markup;
+
+use OnPHP\Core\Exception\WrongArgumentException;
+use OnPHP\Main\Markup\Html\SgmlOpenTag;
+use OnPHP\Main\Markup\Html\SgmlTag;
+use OnPHP\Tests\TestEnvironment\TestCase;
+
+class SgmlOpenTagTest extends TestCase
+{
+	public function testCreate()
+	{
+		$reflectionClass = new \ReflectionClass(SgmlOpenTag::class);
+		$this->assertTrue($reflectionClass->isFinal());
+
+		$tag = SgmlOpenTag::create();
+		$this->assertInstanceOf(SgmlOpenTag::class, $tag);
+		$this->assertEmpty($tag->getAttributesList());
+		$this->assertFalse($tag->isEmpty());
+
+		$tag = new SgmlOpenTag();
+		$this->assertInstanceOf(SgmlOpenTag::class, $tag);
+		$this->assertEmpty($tag->getAttributesList());
+		$this->assertFalse($tag->isEmpty());
+	}
+
+	public function testEmpty()
+	{
+		$tag = SgmlOpenTag::create();
+		$tag->setEmpty(true);
+		$this->assertTrue($tag->isEmpty());
+		$tag->setEmpty(false);
+		$this->assertFalse($tag->isEmpty());
+	}
+
+	public function testAttributes()
+	{
+		$tag = SgmlOpenTag::create();
+		$tag->setAttribute('class', 'active');
+		$this->assertCount(1, $tag->getAttributesList());
+		$this->assertTrue($tag->hasAttribute('class'));
+		$this->assertTrue($tag->hasAttribute('ClasS'));
+		$this->assertEquals('active', $tag->getAttribute('class'));
+		$this->assertEquals($tag->getAttribute('class'), $tag->getAttribute('CLASS'));
+
+		try {
+			$tag->setAttribute('CLASS', 'in-active');
+			$this->fail('excepted WrongArgumentException exception');
+		} catch (\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		$this->assertCount(1, $tag->getAttributesList());
+		$this->assertTrue($tag->hasAttribute('class'));
+		$this->assertTrue($tag->hasAttribute('ClasS'));
+		$this->assertEquals('active', $tag->getAttribute('class'));
+		$this->assertEquals($tag->getAttribute('class'), $tag->getAttribute('CLASS'));
+
+		$tag->setAttribute('data-test', 'in-active');
+		$this->assertTrue($tag->hasAttribute('data-test'));
+		$this->assertCount(2, $tag->getAttributesList());
+		$this->assertEquals('in-active', $tag->getAttribute('data-test'));
+		$this->assertEquals(
+			['class', 'data-test'],
+			array_keys($tag->getAttributesList())
+		);
+		$this->assertEquals(
+			['active', 'in-active'],
+			array_values($tag->getAttributesList())
+		);
+
+		$tag->dropAttribute('DATA-TEST');
+		$this->assertFalse($tag->hasAttribute('data-test'));
+		$this->assertCount(1, $tag->getAttributesList());
+		try {
+			$tag->getAttribute('data-test');
+			$this->fail('excepted WrongArgumentException exception');
+		} catch (\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			$tag->dropAttribute('data-test');
+			$this->fail('excepted WrongArgumentException exception');
+		} catch (\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+
+		$tag->setAttribute('data-test', 'in-active');
+		$this->assertTrue($tag->hasAttribute('DATA-TEST'));
+		$this->assertCount(2, $tag->getAttributesList());
+		$this->assertEquals('in-active', $tag->getAttribute('DATA-TEST'));
+		$tag->dropAttribute('data-test');
+		$this->assertFalse($tag->hasAttribute('data-test'));
+		$this->assertCount(1, $tag->getAttributesList());
+		$tag->setAttribute('data-test', 'in-active');
+		$this->assertCount(2, $tag->getAttributesList());
+		$tag->dropAttributesList();
+		$this->assertEmpty($tag->getAttributesList());
+		try {
+			$tag->getAttribute('data-test');
+			$this->fail('excepted WrongArgumentException exception');
+		} catch (\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+		try {
+			$tag->getAttribute('class');
+			$this->fail('excepted WrongArgumentException exception');
+		} catch (\Throwable $exception) {
+			$this->assertInstanceOf(WrongArgumentException::class, $exception);
+		}
+	}
+}
\ No newline at end of file
diff --git a/tests/Main/Markup/SgmlTagTest.php b/tests/Main/Markup/SgmlTagTest.php
new file mode 100644
index 0000000000..d8a1c1dc94
--- /dev/null
+++ b/tests/Main/Markup/SgmlTagTest.php
@@ -0,0 +1,42 @@
+<?php
+/***************************************************************************
+ *   Copyright (C) 2021 by Sergei V. Deriabin                              *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License as        *
+ *   published by the Free Software Foundation; either version 3 of the    *
+ *   License, or (at your option) any later version.                       *
+ *                                                                         *
+ ***************************************************************************/
+
+namespace OnPHP\Tests\Main\Markup;
+
+use OnPHP\Main\Markup\Html\SgmlTag;
+use OnPHP\Tests\TestEnvironment\TestCase;
+
+class SgmlTagTest extends TestCase
+{
+	public function testCreate()
+	{
+		$reflectionClass = new \ReflectionClass(SgmlTag::class);
+		$this->assertTrue($reflectionClass->isAbstract());
+
+		$tag = \OnPHP\Tests\TestEnvironment\SgmlTag::create();
+		$this->assertInstanceOf(SgmlTag::class, $tag);
+		$this->assertNull($tag->getId());
+
+		$tag = new \OnPHP\Tests\TestEnvironment\SgmlTag();
+		$this->assertInstanceOf(SgmlTag::class, $tag);
+		$this->assertNull($tag->getId());
+	}
+
+	public function testValue()
+	{
+		$tag =
+			\OnPHP\Tests\TestEnvironment\SgmlTag::create()
+				->setId('p');
+		$this->assertEquals('p', $tag->getId());
+		$tag->setId('strong');
+		$this->assertEquals('strong', $tag->getId());
+	}
+}
\ No newline at end of file
diff --git a/tests/Main/Markup/SgmlTokenTest.php b/tests/Main/Markup/SgmlTokenTest.php
new file mode 100644
index 0000000000..92074a38dd
--- /dev/null
+++ b/tests/Main/Markup/SgmlTokenTest.php
@@ -0,0 +1,41 @@
+<?php
+/***************************************************************************
+ *   Copyright (C) 2021 by Sergei V. Deriabin                              *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License as        *
+ *   published by the Free Software Foundation; either version 3 of the    *
+ *   License, or (at your option) any later version.                       *
+ *                                                                         *
+ ***************************************************************************/
+
+namespace OnPHP\Tests\Main\Markup;
+
+use TypeError;
+use OnPHP\Main\Markup\Html\SgmlToken;
+use OnPHP\Tests\TestEnvironment\TestCase;
+
+class SgmlTokenTest extends TestCase
+{
+	public function testCreate()
+	{
+		$token = SgmlToken::create();
+		$this->assertInstanceOf(SgmlToken::class, $token);
+		$this->assertNull($token->getValue());
+
+		$token = new SgmlToken();
+		$this->assertInstanceOf(SgmlToken::class, $token);
+		$this->assertNull($token->getValue());
+	}
+
+	public function testValue()
+	{
+		$token = SgmlToken::create();
+		$token->setValue('test');
+		$this->assertEquals('test', $token->getValue());
+		$token->setValue(null);
+		$this->assertNull($token->getValue());
+		$this->expectException(TypeError::class);
+		$token->setValue(function() { return true; });
+	}
+}
\ No newline at end of file
diff --git a/tests/TestEnvironment/SgmlTag.php b/tests/TestEnvironment/SgmlTag.php
new file mode 100644
index 0000000000..75d8dd3853
--- /dev/null
+++ b/tests/TestEnvironment/SgmlTag.php
@@ -0,0 +1,17 @@
+<?php
+/***************************************************************************
+ *   Copyright (C) 2021 by Sergei V. Deriabin                              *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU Lesser General Public License as        *
+ *   published by the Free Software Foundation; either version 3 of the    *
+ *   License, or (at your option) any later version.                       *
+ *                                                                         *
+ ***************************************************************************/
+
+namespace OnPHP\Tests\TestEnvironment;
+
+class SgmlTag extends \OnPHP\Main\Markup\Html\SgmlTag
+{
+
+}
\ No newline at end of file
diff --git a/tests/TestEnvironment/TestCase.php b/tests/TestEnvironment/TestCase.php
index 0e7de13553..cb0d68d099 100644
--- a/tests/TestEnvironment/TestCase.php
+++ b/tests/TestEnvironment/TestCase.php
@@ -2,10 +2,36 @@
 
 namespace OnPHP\Tests\TestEnvironment;
 
+use ReflectionClass;
 use PHPUnit\Framework\TestCase as PHPUnitTestCase;
 
 abstract class TestCase extends PHPUnitTestCase
 {
 	protected $backupGlobals = false;
-}
-?>
\ No newline at end of file
+
+	/**
+	 * @param object $object
+	 * @param string $parameter
+	 * @return mixed
+	 * @throws \ReflectionException
+	 */
+	protected function getObjectProperty(object $object, string $parameter)
+	{
+		$class = new ReflectionClass($object);
+		$property = $class->getProperty($parameter);
+		$property->setAccessible(true);
+
+		return $property->getValue($object);
+	}
+
+	protected function callObjectMethod($className, string $methodName, ...$args)
+	{
+		$class = new ReflectionClass($className);
+		$method = $class->getMethod($methodName);
+		$method->setAccessible(true);
+		return $method->invokeArgs(
+			is_object($className) ? $className : null,
+			$args
+		);
+	}
+}
\ No newline at end of file