diff --git a/src/Data/AlphaNum.php b/src/Data/AlphaNum.php
index 6c06305f8..28d9d7563 100644
--- a/src/Data/AlphaNum.php
+++ b/src/Data/AlphaNum.php
@@ -18,6 +18,9 @@ use function ord, sprintf;
 
 /**
  * Alphanumeric mode: 0 to 9, A to Z, space, $ % * + - . / :
+ *
+ * ISO/IEC 18004:2000 Section 8.3.3
+ * ISO/IEC 18004:2000 Section 8.4.3
  */
 final class AlphaNum extends QRDataAbstract{
 
@@ -41,7 +44,9 @@ final class AlphaNum extends QRDataAbstract{
 	}
 
 	/**
-	 * @throws \chillerlan\QRCode\Data\QRCodeDataException
+	 * get the code for the given character
+	 *
+	 * @throws \chillerlan\QRCode\Data\QRCodeDataException on an illegal character occurence
 	 */
 	protected function getCharCode(string $chr):int{
 
diff --git a/src/Data/Byte.php b/src/Data/Byte.php
index b4fe4309c..02e76a639 100644
--- a/src/Data/Byte.php
+++ b/src/Data/Byte.php
@@ -18,6 +18,9 @@ use function ord;
 
 /**
  * Byte mode, ISO-8859-1 or UTF-8
+ *
+ * ISO/IEC 18004:2000 Section 8.3.4
+ * ISO/IEC 18004:2000 Section 8.4.4
  */
 final class Byte extends QRDataAbstract{
 
diff --git a/src/Data/Kanji.php b/src/Data/Kanji.php
index 12f7a6b7c..b08af0776 100644
--- a/src/Data/Kanji.php
+++ b/src/Data/Kanji.php
@@ -18,6 +18,9 @@ use function mb_strlen, ord, sprintf, strlen;
 
 /**
  * Kanji mode: double-byte characters from the Shift JIS character set
+ *
+ * ISO/IEC 18004:2000 Section 8.3.5
+ * ISO/IEC 18004:2000 Section 8.4.5
  */
 final class Kanji extends QRDataAbstract{
 
@@ -34,6 +37,8 @@ final class Kanji extends QRDataAbstract{
 
 	/**
 	 * @inheritdoc
+	 *
+	 * @throws \chillerlan\QRCode\Data\QRCodeDataException on an illegal character occurence
 	 */
 	protected function write(string $data):void{
 		$len = strlen($data);
diff --git a/src/Data/MaskPatternTester.php b/src/Data/MaskPatternTester.php
index 963f62e21..ae8972b9a 100644
--- a/src/Data/MaskPatternTester.php
+++ b/src/Data/MaskPatternTester.php
@@ -17,12 +17,15 @@ use function abs, array_search, call_user_func_array, min;
 /**
  * Receives a QRDataInterface object and runs the mask pattern tests on it.
  *
- * @link http://www.thonky.com/qr-code-tutorial/data-masking
+ * ISO/IEC 18004:2000 Section 8.8.2 - Evaluation of masking results
+ *
+ * @see http://www.thonky.com/qr-code-tutorial/data-masking
  */
 final class MaskPatternTester{
 
-	protected QRMatrix $matrix;
-
+	/**
+	 * The data interface that contains the data matrix to test
+	 */
 	protected QRDataInterface $dataInterface;
 
 	/**
@@ -153,7 +156,7 @@ final class MaskPatternTester{
 	}
 
 	/**
-	 * Checks if there are patterns that look similar to the finder patterns
+	 * Checks if there are patterns that look similar to the finder patterns (1:1:3:1:1 ratio)
 	 */
 	protected function testLevel3(QRMatrix $m, int $size):float{
 		$penalty = 0;
diff --git a/src/Data/Number.php b/src/Data/Number.php
index fa1107050..dedc54a39 100644
--- a/src/Data/Number.php
+++ b/src/Data/Number.php
@@ -4,7 +4,7 @@
  *
  * @filesource   Number.php
  * @created      26.11.2015
- * @package      QRCode
+ * @package      chillerlan\QRCode\Data
  * @author       Smiley <smiley@chillerlan.net>
  * @copyright    2015 Smiley
  * @license      MIT
@@ -17,7 +17,10 @@ use chillerlan\QRCode\QRCode;
 use function ord, sprintf, substr;
 
 /**
- * Numeric mode: decimal digits 0 through 9
+ * Numeric mode: decimal digits 0 to 9
+ *
+ * ISO/IEC 18004:2000 Section 8.3.2
+ * ISO/IEC 18004:2000 Section 8.4.2
  */
 final class Number extends QRDataAbstract{
 
@@ -50,12 +53,14 @@ final class Number extends QRDataAbstract{
 	}
 
 	/**
-	 * @throws \chillerlan\QRCode\Data\QRCodeDataException
+	 * get the code for the given numeric string
+	 *
+	 * @throws \chillerlan\QRCode\Data\QRCodeDataException on an illegal character occurence
 	 */
 	protected function parseInt(string $string):int{
 		$num = 0;
-
 		$len = strlen($string);
+
 		for($i = 0; $i < $len; $i++){
 			$c = ord($string[$i]);
 
diff --git a/src/Data/QRDataAbstract.php b/src/Data/QRDataAbstract.php
index 5c4e3f68f..6fda7dac2 100644
--- a/src/Data/QRDataAbstract.php
+++ b/src/Data/QRDataAbstract.php
@@ -35,6 +35,8 @@ abstract class QRDataAbstract implements QRDataInterface{
 
 	/**
 	 * mode length bits for the version breakpoints 1-9, 10-26 and 27-40
+	 *
+	 * ISO/IEC 18004:2000 Table 3 - Number of bits in Character Count Indicator
 	 */
 	protected array $lengthBits = [0, 0, 0];
 
@@ -166,7 +168,7 @@ abstract class QRDataAbstract implements QRDataInterface{
 	/**
 	 * creates a BitBuffer and writes the string data to it
 	 *
-	 * @throws \chillerlan\QRCode\QRCodeException
+	 * @throws \chillerlan\QRCode\QRCodeException on data overflow
 	 */
 	protected function writeBitBuffer(string $data):void{
 		$this->bitBuffer = new BitBuffer;
@@ -186,7 +188,7 @@ abstract class QRDataAbstract implements QRDataInterface{
 			throw new QRCodeDataException(sprintf('code length overflow. (%d > %d bit)', $this->bitBuffer->getLength(), $MAX_BITS));
 		}
 
-		// end code.
+		// add terminator (ISO/IEC 18004:2000 Table 2)
 		if($this->bitBuffer->getLength() + 4 <= $MAX_BITS){
 			$this->bitBuffer->put(0, 4);
 		}
@@ -217,7 +219,9 @@ abstract class QRDataAbstract implements QRDataInterface{
 	/**
 	 * ECC masking
 	 *
-	 * @link http://www.thonky.com/qr-code-tutorial/error-correction-coding
+	 * ISO/IEC 18004:2000 Section 8.5 ff
+	 *
+	 * @see http://www.thonky.com/qr-code-tutorial/error-correction-coding
 	 */
 	protected function maskECC():array{
 		[$l1, $l2, $b1, $b2] = $this::RSBLOCKS[$this->version][QRCode::ECC_MODES[$this->options->eccLevel]];
@@ -282,7 +286,7 @@ abstract class QRDataAbstract implements QRDataInterface{
 	}
 
 	/**
-	 *
+	 * helper method for the polynomial operations
 	 */
 	protected function poly(int $key, int $count):array{
 		$rsPoly  = new Polynomial;
diff --git a/src/Data/QRDataInterface.php b/src/Data/QRDataInterface.php
index 8f99fbcdb..cc86f7cd6 100644
--- a/src/Data/QRDataInterface.php
+++ b/src/Data/QRDataInterface.php
@@ -13,16 +13,22 @@
 namespace chillerlan\QRCode\Data;
 
 /**
- *
+ * Specifies the methods reqired for the data modules (Number, Alphanum, Byte and Kanji)
+ * and holds version information in several constants
  */
 interface QRDataInterface{
 
+	/**
+	 * @var int[]
+	 */
 	const CHAR_MAP_NUMBER = [
 		'0' => 0, '1' => 1, '2' => 2, '3' => 3, '4' => 4, '5' => 5, '6' => 6, '7' => 7, '8' => 8, '9' => 9,
 	];
 
 	/**
 	 * ISO/IEC 18004:2000 Table 5
+	 *
+	 * @var int[]
 	 */
 	const CHAR_MAP_ALPHANUM = [
 		'0' =>  0, '1' =>  1, '2' =>  2, '3' =>  3, '4' =>  4, '5' =>  5, '6' =>  6, '7' =>  7,
@@ -34,7 +40,11 @@ interface QRDataInterface{
 	];
 
 	/**
-	 * @link http://www.qrcode.com/en/about/version.html
+	 * ISO/IEC 18004:2000 Tables 7-11 - Number of symbol characters and input data capacity for versions 1 to 40
+	 *
+	 * @see http://www.qrcode.com/en/about/version.html
+	 *
+	 * @var int [][][]
 	 */
 	const MAX_LENGTH =[
 	//	v  => [NUMERIC => [L, M, Q, H ], ALPHANUM => [L, M, Q, H], BINARY => [L, M, Q, H  ], KANJI => [L, M, Q, H   ]]  // modules
@@ -80,6 +90,11 @@ interface QRDataInterface{
 		40 => [[7089, 5596, 3993, 3057], [4296, 3391, 2420, 1852], [2953, 2331, 1663, 1273], [1817, 1435, 1024,  784]], // 177
 	];
 
+	/**
+	 * ISO/IEC 18004:2000 Tables 7-11 - Number of symbol characters and input data capacity for versions 1 to 40
+	 *
+	 * @var int [][]
+	 */
 	const MAX_BITS = [
 		// version => [L, M, Q, H ]
 		1  => [  152,   128,   104,    72],
@@ -125,7 +140,9 @@ interface QRDataInterface{
 	];
 
 	/**
-	 * @link http://www.thonky.com/qr-code-tutorial/error-correction-table
+	 * @see http://www.thonky.com/qr-code-tutorial/error-correction-table
+	 *
+	 * @var int [][][]
 	 */
 	const RSBLOCKS = [
 		1  => [[ 1,  0,  26,  19], [ 1,  0, 26, 16], [ 1,  0, 26, 13], [ 1,  0, 26,  9]],
diff --git a/src/Data/QRMatrix.php b/src/Data/QRMatrix.php
index 8fd056c8d..8a52e98de 100755
--- a/src/Data/QRMatrix.php
+++ b/src/Data/QRMatrix.php
@@ -18,28 +18,44 @@ use Closure;
 use function array_fill, array_key_exists, array_push, array_unshift, count, floor, in_array, max, min, range;
 
 /**
- * @link http://www.thonky.com/qr-code-tutorial/format-version-information
+ * Holds a numerical representation of the final QR Code;
+ * maps the ECC coded binary data and applies the mask pattern
+ *
+ * @see http://www.thonky.com/qr-code-tutorial/format-version-information
  */
 final class QRMatrix{
 
+	/** @var int */
 	public const M_NULL       = 0x00;
+	/** @var int */
 	public const M_DARKMODULE = 0x02;
+	/** @var int */
 	public const M_DATA       = 0x04;
+	/** @var int */
 	public const M_FINDER     = 0x06;
+	/** @var int */
 	public const M_SEPARATOR  = 0x08;
+	/** @var int */
 	public const M_ALIGNMENT  = 0x0a;
+	/** @var int */
 	public const M_TIMING     = 0x0c;
+	/** @var int */
 	public const M_FORMAT     = 0x0e;
+	/** @var int */
 	public const M_VERSION    = 0x10;
+	/** @var int */
 	public const M_QUIETZONE  = 0x12;
-#	public const M_LOGO       = 0x14; // @todo
 
+#	public const M_LOGO       = 0x14; // @todo
+	/** @var int */
 	public const M_TEST       = 0xff;
 
 	/**
-	 * @link http://www.thonky.com/qr-code-tutorial/alignment-pattern-locations
+	 * ISO/IEC 18004:2000 Annex E, Table E.1 - Row/column coordinates of center module of Alignment Patterns
 	 *
-	 *  version -> pattern
+	 * version -> pattern
+	 *
+	 * @var int[][]
 	 */
 	protected const alignmentPattern = [
 		1  => [],
@@ -85,9 +101,11 @@ final class QRMatrix{
 	];
 
 	/**
-	 * @link http://www.thonky.com/qr-code-tutorial/format-version-tables
+	 * ISO/IEC 18004:2000 Annex D, Table D.1 - Version information bit stream for each version
 	 *
 	 * no version pattern for QR Codes < 7
+	 *
+	 * @var int[]
 	 */
 	protected const versionPattern = [
 		7  => 0b000111110010010100,
@@ -126,7 +144,13 @@ final class QRMatrix{
 		40 => 0b101000110001101001,
 	];
 
-	// ECC level -> mask pattern
+	/**
+	 * ISO/IEC 18004:2000 Section 8.9 - Format Information
+	 *
+	 * ECC level -> mask pattern
+	 *
+	 * @var int[][]
+	 */
 	protected const formatPattern = [
 		[ // L
 			0b111011111000100,
@@ -170,14 +194,31 @@ final class QRMatrix{
 		],
 	];
 
+	/**
+	 * the current QR Code version number
+	 */
 	protected int $version;
 
+	/**
+	 * the current ECC level
+	 */
 	protected int $eclevel;
 
+	/**
+	 * the used mask pattern, set via QRMatrix::mapData()
+	 */
 	protected int $maskPattern = QRCode::MASK_PATTERN_AUTO;
 
+	/**
+	 * the size (side length) of the matrix
+	 */
 	protected int $moduleCount;
-	/** @var mixed[] */
+
+	/**
+	 * the actual matrix data array
+	 *
+	 * @var int[][]
+	 */
 	protected array $matrix;
 
 	/**
@@ -217,6 +258,8 @@ final class QRMatrix{
 	}
 
 	/**
+	 * Returns the data matrix
+	 *
 	 * @return int[][]
 	 */
 	public function matrix():array{
@@ -224,21 +267,21 @@ final class QRMatrix{
 	}
 
 	/**
-	 *
+	 * Returns the current version number
 	 */
 	public function version():int{
 		return $this->version;
 	}
 
 	/**
-	 *
+	 * Returns the current ECC level
 	 */
 	public function eccLevel():int{
 		return $this->eclevel;
 	}
 
 	/**
-	 *
+	 * Returns the current mask pattern
 	 */
 	public function maskPattern():int{
 		return $this->maskPattern;
@@ -297,6 +340,8 @@ final class QRMatrix{
 
 	/**
 	 * Draws the 7x7 finder patterns in the corners top left/right and bottom left
+	 *
+	 * ISO/IEC 18004:2000 Section 7.3.2
 	 */
 	public function setFinderPattern():QRMatrix{
 
@@ -324,6 +369,8 @@ final class QRMatrix{
 
 	/**
 	 * Draws the separator lines around the finder patterns
+	 *
+	 * ISO/IEC 18004:2000 Section 7.3.3
 	 */
 	public function setSeparators():QRMatrix{
 
@@ -352,6 +399,8 @@ final class QRMatrix{
 
 	/**
 	 * Draws the 5x5 alignment patterns
+	 *
+	 * ISO/IEC 18004:2000 Section 7.3.5
 	 */
 	public function setAlignmentPattern():QRMatrix{
 
@@ -380,6 +429,8 @@ final class QRMatrix{
 
 	/**
 	 * Draws the timing pattern (h/v checkered line between the finder patterns)
+	 *
+	 * ISO/IEC 18004:2000 Section 7.3.4
 	 */
 	public function setTimingPattern():QRMatrix{
 
@@ -400,6 +451,8 @@ final class QRMatrix{
 
 	/**
 	 * Draws the version information, 2x 3x6 pixel
+	 *
+	 * ISO/IEC 18004:2000 Section 8.10
 	 */
 	public function setVersionNumber(bool $test = null):QRMatrix{
 		$bits = $this::versionPattern[$this->version] ?? false;
@@ -422,6 +475,8 @@ final class QRMatrix{
 
 	/**
 	 * Draws the format info along the finder patterns
+	 *
+	 * ISO/IEC 18004:2000 Section 8.9
 	 */
 	public function setFormatInfo(int $maskPattern, bool $test = null):QRMatrix{
 		$bits = $this::formatPattern[QRCode::ECC_MODES[$this->eclevel]][$maskPattern] ?? 0;
@@ -459,6 +514,8 @@ final class QRMatrix{
 	/**
 	 * Draws the "quiet zone" of $size around the matrix
 	 *
+	 * ISO/IEC 18004:2000 Section 7.3.7
+	 *
 	 * @throws \chillerlan\QRCode\Data\QRCodeDataException
 	 */
 	public function setQuietZone(int $size = null):QRMatrix{
@@ -498,6 +555,8 @@ final class QRMatrix{
 	 *
 	 * @param int[] $data
 	 * @param int   $maskPattern
+	 *
+	 * @return \chillerlan\QRCode\Data\QRMatrix
 	 */
 	public function mapData(array $data, int $maskPattern):QRMatrix{
 		$this->maskPattern = $maskPattern;
diff --git a/src/Helpers/BitBuffer.php b/src/Helpers/BitBuffer.php
index c35abd31c..de47f20f4 100644
--- a/src/Helpers/BitBuffer.php
+++ b/src/Helpers/BitBuffer.php
@@ -14,15 +14,25 @@ namespace chillerlan\QRCode\Helpers;
 
 use function count, floor;
 
+/**
+ * Holds the raw binary data
+ */
 final class BitBuffer{
 
-	/** @var int[] */
+	/**
+	 * The buffer content
+	 *
+	 * @var int[]
+	 */
 	protected array $buffer = [];
 
+	/**
+	 * Length of the content (bits)
+	 */
 	protected int $length = 0;
 
 	/**
-	 *
+	 * clears the buffer
 	 */
 	public function clear():BitBuffer{
 		$this->buffer = [];
@@ -32,7 +42,7 @@ final class BitBuffer{
 	}
 
 	/**
-	 *
+	 * appends a sequence of bits
 	 */
 	public function put(int $num, int $length):BitBuffer{
 
@@ -44,7 +54,7 @@ final class BitBuffer{
 	}
 
 	/**
-	 *
+	 * appends a single bit
 	 */
 	public function putBit(bool $bit):BitBuffer{
 		$bufIndex = floor($this->length / 8);
diff --git a/src/Helpers/Polynomial.php b/src/Helpers/Polynomial.php
index 12c3f0078..c42e0831c 100644
--- a/src/Helpers/Polynomial.php
+++ b/src/Helpers/Polynomial.php
@@ -17,12 +17,14 @@ use chillerlan\QRCode\QRCodeException;
 use function array_fill, count, sprintf;
 
 /**
- * @link http://www.thonky.com/qr-code-tutorial/error-correction-coding
+ * Polynomial long division helpers
+ *
+ * @see http://www.thonky.com/qr-code-tutorial/error-correction-coding
  */
 final class Polynomial{
 
 	/**
-	 * @link http://www.thonky.com/qr-code-tutorial/log-antilog-table
+	 * @see http://www.thonky.com/qr-code-tutorial/log-antilog-table
 	 */
 	protected const table = [
 		[  1,   0], [  2,   0], [  4,   1], [  8,  25], [ 16,   2], [ 32,  50], [ 64,  26], [128, 198],
@@ -79,7 +81,10 @@ final class Polynomial{
 	}
 
 	/**
+	 * @param int[]    $num
+	 * @param int|null $shift
 	 *
+	 * @return \chillerlan\QRCode\Helpers\Polynomial
 	 */
 	public function setNum(array $num, int $shift = null):Polynomial{
 		$offset = 0;
@@ -99,7 +104,9 @@ final class Polynomial{
 	}
 
 	/**
+	 * @param int[] $e
 	 *
+	 * @return \chillerlan\QRCode\Helpers\Polynomial
 	 */
 	public function multiply(array $e):Polynomial{
 		$n = array_fill(0, count($this->num) + count($e) - 1, 0);
@@ -119,7 +126,9 @@ final class Polynomial{
 	}
 
 	/**
+	 * @param int[] $e
 	 *
+	 * @return \chillerlan\QRCode\Helpers\Polynomial
 	 */
 	public function mod(array $e):Polynomial{
 		$n = $this->num;
diff --git a/src/Output/QRImage.php b/src/Output/QRImage.php
index f64f64160..f30a87552 100644
--- a/src/Output/QRImage.php
+++ b/src/Output/QRImage.php
@@ -20,12 +20,17 @@ use function array_values, base64_encode, call_user_func, count, imagecoloralloc
 	is_array, ob_end_clean, ob_get_contents, ob_start, range, sprintf;
 
 /**
- * Converts the matrix into GD images, raw or base64 output
- * requires ext-gd
- * @link http://php.net/manual/book.image.php
+ * Converts the matrix into GD images, raw or base64 output (requires ext-gd)
+ *
+ * @see http://php.net/manual/book.image.php
  */
 class QRImage extends QROutputAbstract{
 
+	/**
+	 * GD image types that support transparency
+	 *
+	 * @var string[]
+	 */
 	protected const TRANSPARENCY_TYPES = [
 		QRCode::OUTPUT_IMAGE_PNG,
 		QRCode::OUTPUT_IMAGE_GIF,
@@ -34,6 +39,8 @@ class QRImage extends QROutputAbstract{
 	protected string $defaultMode = QRCode::OUTPUT_IMAGE_PNG;
 
 	/**
+	 * The GD image resource
+	 *
 	 * @see imagecreatetruecolor()
 	 * @var resource
 	 */
@@ -70,8 +77,8 @@ class QRImage extends QROutputAbstract{
 
 		// avoid: Indirect modification of overloaded property $imageTransparencyBG has no effect
 		// https://stackoverflow.com/a/10455217
-		$tbg = $this->options->imageTransparencyBG;
-		$background  = imagecolorallocate($this->image, ...$tbg);
+		$tbg        = $this->options->imageTransparencyBG;
+		$background = imagecolorallocate($this->image, ...$tbg);
 
 		if((bool)$this->options->imageTransparent && in_array($this->options->outputType, $this::TRANSPARENCY_TYPES, true)){
 			imagecolortransparent($this->image, $background);
@@ -99,7 +106,7 @@ class QRImage extends QROutputAbstract{
 	}
 
 	/**
-	 *
+	 * Creates a single QR pixel with the given settings
 	 */
 	protected function setPixel(int $x, int $y, array $rgb):void{
 		imagefilledrectangle(
@@ -113,7 +120,7 @@ class QRImage extends QROutputAbstract{
 	}
 
 	/**
-	 * @param string|null $file
+	 * Creates the final image by calling the desired GD output function
 	 *
 	 * @throws \chillerlan\QRCode\Output\QRCodeOutputException
 	 */
@@ -139,6 +146,8 @@ class QRImage extends QROutputAbstract{
 	}
 
 	/**
+	 * PNG output
+	 *
 	 * @return void
 	 */
 	protected function png():void{
@@ -153,6 +162,7 @@ class QRImage extends QROutputAbstract{
 
 	/**
 	 * Jiff - like... JitHub!
+	 *
 	 * @return void
 	 */
 	protected function gif():void{
@@ -160,6 +170,8 @@ class QRImage extends QROutputAbstract{
 	}
 
 	/**
+	 * JPG output
+	 *
 	 * @return void
 	 */
 	protected function jpg():void{
diff --git a/src/Output/QRImagick.php b/src/Output/QRImagick.php
index 0a31b3169..9afd5df40 100644
--- a/src/Output/QRImagick.php
+++ b/src/Output/QRImagick.php
@@ -8,6 +8,8 @@
  * @author       smiley <smiley@chillerlan.net>
  * @copyright    2018 smiley
  * @license      MIT
+ *
+ * @noinspection PhpComposerExtensionStubsInspection
  */
 
 namespace chillerlan\QRCode\Output;
@@ -17,10 +19,10 @@ use Imagick, ImagickDraw, ImagickPixel;
 use function is_string;
 
 /**
- * ImageMagick output module
- * requires ext-imagick
- * @link http://php.net/manual/book.imagick.php
- * @link http://phpimagick.com
+ * ImageMagick output module (requires ext-imagick)
+ *
+ * @see http://php.net/manual/book.imagick.php
+ * @see http://phpimagick.com
  */
 class QRImagick extends QROutputAbstract{
 
@@ -67,7 +69,7 @@ class QRImagick extends QROutputAbstract{
 	}
 
 	/**
-	 *
+	 * Creates the QR image via ImagickDraw
 	 */
 	protected function drawImage(Imagick $imagick):string{
 		$draw = new ImagickDraw;
diff --git a/src/Output/QRMarkup.php b/src/Output/QRMarkup.php
index f7abeb6c5..8eb83e0ed 100644
--- a/src/Output/QRMarkup.php
+++ b/src/Output/QRMarkup.php
@@ -26,7 +26,8 @@ class QRMarkup extends QROutputAbstract{
 	/**
 	 * @see \sprintf()
 	 */
-	protected string $svgHeader = '<svg xmlns="http://www.w3.org/2000/svg" version="1.1" class="qr-svg %1$s" style="width: 100%%; height: auto;" viewBox="0 0 %2$d %2$d">';
+	protected string $svgHeader = '<svg xmlns="http://www.w3.org/2000/svg" class="qr-svg %1$s" '.
+	                              'style="width: 100%%; height: auto;" viewBox="0 0 %2$d %2$d">';
 
 	/**
 	 * @inheritDoc
@@ -50,7 +51,7 @@ class QRMarkup extends QROutputAbstract{
 	}
 
 	/**
-	 *
+	 * HTML output
 	 */
 	protected function html():string{
 		$html = '<div class="'.$this->options->cssClass.'">'.$this->options->eol;
@@ -68,14 +69,18 @@ class QRMarkup extends QROutputAbstract{
 		$html .= '</div>'.$this->options->eol;
 
 		if($this->options->cachefile){
-			return '<!DOCTYPE html><head><meta charset="UTF-8"></head><body>'.$this->options->eol.$html.'</body>';
+			return '<!DOCTYPE html>'.
+			       '<head><meta charset="UTF-8"><title>QR Code</title></head>'.
+			       '<body>'.$this->options->eol.$html.'</body>';
 		}
 
 		return $html;
 	}
 
 	/**
-	 * @link https://github.com/codemasher/php-qrcode/pull/5
+	 * SVG output
+	 *
+	 * @see https://github.com/codemasher/php-qrcode/pull/5
 	 */
 	protected function svg():string{
 		$matrix = $this->matrix->matrix();
@@ -123,7 +128,10 @@ class QRMarkup extends QROutputAbstract{
 			}
 
 			if(!empty($path)){
-				$svg .= sprintf('<path class="qr-%s %s" stroke="transparent" fill="%s" fill-opacity="%s" d="%s" />', $M_TYPE, $this->options->cssClass, $value, $this->options->svgOpacity, $path);
+				$svg .= sprintf(
+					'<path class="qr-%s %s" stroke="transparent" fill="%s" fill-opacity="%s" d="%s" />',
+					$M_TYPE, $this->options->cssClass, $value, $this->options->svgOpacity, $path
+				);
 			}
 
 		}
@@ -133,7 +141,8 @@ class QRMarkup extends QROutputAbstract{
 
 		// if saving to file, append the correct headers
 		if($this->options->cachefile){
-			return '<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">'.$this->options->eol.$svg;
+			return '<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">'.
+			       $this->options->eol.$svg;
 		}
 
 		return $svg;
diff --git a/src/Output/QRString.php b/src/Output/QRString.php
index 036978984..3f668f80e 100644
--- a/src/Output/QRString.php
+++ b/src/Output/QRString.php
@@ -45,7 +45,7 @@ class QRString extends QROutputAbstract{
 	}
 
 	/**
-	 *
+	 * string output
 	 */
 	protected function text():string{
 		$str = [];
@@ -64,7 +64,7 @@ class QRString extends QROutputAbstract{
 	}
 
 	/**
-	 *
+	 * JSON output
 	 */
 	protected function json():string{
 		return json_encode($this->matrix->matrix());
diff --git a/src/QRCode.php b/src/QRCode.php
index c46a40371..12b0a76d3 100755
--- a/src/QRCode.php
+++ b/src/QRCode.php
@@ -25,45 +25,37 @@ use function call_user_func_array, class_exists, in_array, mb_internal_encoding,
 /**
  * Turns a text string into a Model 2 QR Code
  *
- * @link https://github.com/kazuhikoarase/qrcode-generator/tree/master/php
- * @link http://www.qrcode.com/en/codes/model12.html
- * @link http://www.thonky.com/qr-code-tutorial/
+ * @see https://github.com/kazuhikoarase/qrcode-generator/tree/master/php
+ * @see http://www.qrcode.com/en/codes/model12.html
+ * @see https://www.swisseduc.ch/informatik/theoretische_informatik/qr_codes/docs/qr_standard.pdf
+ * @see https://en.wikipedia.org/wiki/QR_code
+ * @see http://www.thonky.com/qr-code-tutorial/
  */
 class QRCode{
 
-	/**
-	 * API constants
-	 */
-	public const OUTPUT_MARKUP_HTML = 'html';
-	public const OUTPUT_MARKUP_SVG  = 'svg';
-	public const OUTPUT_IMAGE_PNG   = 'png';
-	public const OUTPUT_IMAGE_JPG   = 'jpg';
-	public const OUTPUT_IMAGE_GIF   = 'gif';
-	public const OUTPUT_STRING_JSON = 'json';
-	public const OUTPUT_STRING_TEXT = 'text';
-	public const OUTPUT_IMAGICK     = 'imagick';
-	public const OUTPUT_CUSTOM      = 'custom';
-
+	/** @var int */
 	public const VERSION_AUTO       = -1;
+	/** @var int */
 	public const MASK_PATTERN_AUTO  = -1;
 
-	public const ECC_L         = 0b01; // 7%.
-	public const ECC_M         = 0b00; // 15%.
-	public const ECC_Q         = 0b11; // 25%.
-	public const ECC_H         = 0b10; // 30%.
+	// ISO/IEC 18004:2000 Table 2
 
+	/** @var int */
 	public const DATA_NUMBER   = 0b0001;
+	/** @var int */
 	public const DATA_ALPHANUM = 0b0010;
+	/** @var int */
 	public const DATA_BYTE     = 0b0100;
+	/** @var int */
 	public const DATA_KANJI    = 0b1000;
 
-	public const ECC_MODES = [
-		self::ECC_L => 0,
-		self::ECC_M => 1,
-		self::ECC_Q => 2,
-		self::ECC_H => 3,
-	];
-
+	/**
+	 * References to the keys of the following tables:
+	 *
+	 * @see \chillerlan\QRCode\Data\QRDataInterface::MAX_LENGTH
+	 *
+	 * @var int[]
+	 */
 	public const DATA_MODES = [
 		self::DATA_NUMBER   => 0,
 		self::DATA_ALPHANUM => 1,
@@ -71,6 +63,57 @@ class QRCode{
 		self::DATA_KANJI    => 3,
 	];
 
+	// ISO/IEC 18004:2000 Tables 12, 25
+
+	/** @var int */
+	public const ECC_L = 0b01; // 7%.
+	/** @var int */
+	public const ECC_M = 0b00; // 15%.
+	/** @var int */
+	public const ECC_Q = 0b11; // 25%.
+	/** @var int */
+	public const ECC_H = 0b10; // 30%.
+
+	/**
+	 * References to the keys of the following tables:
+	 *
+	 * @see \chillerlan\QRCode\Data\QRDataInterface::MAX_BITS
+	 * @see \chillerlan\QRCode\Data\QRDataInterface::RSBLOCKS
+	 * @see \chillerlan\QRCode\Data\QRMatrix::formatPattern
+	 *
+	 * @var int[]
+	 */
+	public const ECC_MODES = [
+		self::ECC_L => 0,
+		self::ECC_M => 1,
+		self::ECC_Q => 2,
+		self::ECC_H => 3,
+	];
+
+	/** @var string */
+	public const OUTPUT_MARKUP_HTML = 'html';
+	/** @var string */
+	public const OUTPUT_MARKUP_SVG  = 'svg';
+	/** @var string */
+	public const OUTPUT_IMAGE_PNG   = 'png';
+	/** @var string */
+	public const OUTPUT_IMAGE_JPG   = 'jpg';
+	/** @var string */
+	public const OUTPUT_IMAGE_GIF   = 'gif';
+	/** @var string */
+	public const OUTPUT_STRING_JSON = 'json';
+	/** @var string */
+	public const OUTPUT_STRING_TEXT = 'text';
+	/** @var string */
+	public const OUTPUT_IMAGICK     = 'imagick';
+	/** @var string */
+	public const OUTPUT_CUSTOM      = 'custom';
+
+	/**
+	 * Map of built-in output modules => capabilities
+	 *
+	 * @var string[][]
+	 */
 	public const OUTPUT_MODES = [
 		QRMarkup::class => [
 			self::OUTPUT_MARKUP_SVG,
@@ -103,22 +146,31 @@ class QRCode{
 	];
 
 	/**
+	 * The settings container
+	 *
 	 * @var \chillerlan\QRCode\QROptions|\chillerlan\Settings\SettingsContainerInterface
 	 */
 	protected SettingsContainerInterface $options;
 
+	/**
+	 * The selected data interface (Number, AlphaNum, Kanji, Byte)
+	 */
 	protected QRDataInterface $dataInterface;
 
 	/**
-	 * @see http://php.net/manual/function.mb-internal-encoding.php
+	 * The current encoding (before the QRCode instance was invoked)
+	 *
+	 * @see http://php.net/manual/function.mb-internal-encoding.php mb_internal_encoding()
 	 */
 	protected string $mbCurrentEncoding;
 
 	/**
 	 * QRCode constructor.
+	 *
+	 * Sets the options instance, determines the current mb-encoding and sets it to UTF-8
 	 */
 	public function __construct(SettingsContainerInterface $options = null){
-		// save the current mb encoding (in case it differs from UTF-8)
+		// save the current mb-encoding (in case it differs from UTF-8)
 		$this->mbCurrentEncoding = mb_internal_encoding();
 		// use UTF-8 from here on
 		mb_internal_encoding('UTF-8');
@@ -127,10 +179,11 @@ class QRCode{
 	}
 
 	/**
+	 * Restores the previous mb-encoding setting, so that we don't mess up the rest of the script
+	 *
 	 * @return void
 	 */
 	public function __destruct(){
-		// restore the previous mb_internal_encoding, so that we don't mess up the rest of the script
 		mb_internal_encoding($this->mbCurrentEncoding);
 	}
 
diff --git a/src/QRCodeException.php b/src/QRCodeException.php
index 68af380ff..55bb1be4b 100644
--- a/src/QRCodeException.php
+++ b/src/QRCodeException.php
@@ -12,4 +12,7 @@
 
 namespace chillerlan\QRCode;
 
+/**
+ * An exception container
+ */
 class QRCodeException extends \Exception{}
diff --git a/src/QROptions.php b/src/QROptions.php
index 8e20626c5..79242245d 100644
--- a/src/QROptions.php
+++ b/src/QROptions.php
@@ -15,43 +15,37 @@ namespace chillerlan\QRCode;
 use chillerlan\Settings\SettingsContainerAbstract;
 
 /**
- * @property int    $version
- * @property int    $versionMin
- * @property int    $versionMax
- * @property int    $eccLevel
- * @property int    $maskPattern
- * @property bool   $addQuietzone
- * @property int    $quietzoneSize
+ * The QRCode settings container
  *
- * @property string $dataMode
- * @property string $outputType
- * @property string $outputInterface
- * @property string $cachefile
- *
- * @property string $eol
- * @property int    $scale
- *
- * @property string $cssClass
- * @property float  $svgOpacity
- * @property string $svgDefs
- * @property int    $svgViewBoxSize
- *
- * @property string $textDark
- * @property string $textLight
- *
- * @property string $markupDark
- * @property string $markupLight
- *
- * @property bool   $imageBase64
- * @property bool   $imageTransparent
- * @property array  $imageTransparencyBG
- * @property int    $pngCompression
- * @property int    $jpegQuality
- *
- * @property string $imagickFormat
- * @property string $imagickBG
- *
- * @property array  $moduleValues
+ * @property int         $version
+ * @property int         $versionMin
+ * @property int         $versionMax
+ * @property int         $eccLevel
+ * @property int         $maskPattern
+ * @property bool        $addQuietzone
+ * @property int         $quietzoneSize
+ * @property string|null $dataMode
+ * @property string      $outputType
+ * @property string|null $outputInterface
+ * @property string|null $cachefile
+ * @property string      $eol
+ * @property int         $scale
+ * @property string      $cssClass
+ * @property float       $svgOpacity
+ * @property string      $svgDefs
+ * @property int         $svgViewBoxSize
+ * @property string      $textDark
+ * @property string      $textLight
+ * @property string      $markupDark
+ * @property string      $markupLight
+ * @property bool        $imageBase64
+ * @property bool        $imageTransparent
+ * @property array       $imageTransparencyBG
+ * @property int         $pngCompression
+ * @property int         $jpegQuality
+ * @property string      $imagickFormat
+ * @property string|null $imagickBG
+ * @property array|null  $moduleValues
  */
 class QROptions extends SettingsContainerAbstract{
 	use QROptionsTrait;
diff --git a/src/QROptionsTrait.php b/src/QROptionsTrait.php
index cadc32877..fc29bb3f7 100644
--- a/src/QROptionsTrait.php
+++ b/src/QROptionsTrait.php
@@ -14,17 +14,22 @@ namespace chillerlan\QRCode;
 
 use function array_values, count, is_numeric, max, min, sprintf;
 
+/**
+ * The QRCode plug-in settings & setter functionality
+ */
 trait QROptionsTrait{
 
 	/**
 	 * QR Code version number
 	 *
-	 *   [1 ... 40] or QRCode::VERSION_AUTO
+	 * [1 ... 40] or QRCode::VERSION_AUTO
 	 */
 	protected int $version = QRCode::VERSION_AUTO;
 
 	/**
-	 * Minimum QR version (if $version = QRCode::VERSION_AUTO)
+	 * Minimum QR version
+	 *
+	 * if $version = QRCode::VERSION_AUTO
 	 */
 	protected int $versionMin = 1;
 
@@ -36,18 +41,19 @@ trait QROptionsTrait{
 	/**
 	 * Error correct level
 	 *
-	 *   QRCode::ECC_X where X is
-	 *    L =>  7%
-	 *    M => 15%
-	 *    Q => 25%
-	 *    H => 30%
+	 * QRCode::ECC_X where X is:
+	 *
+	 *   - L =>  7%
+	 *   - M => 15%
+	 *   - Q => 25%
+	 *   - H => 30%
 	 */
 	protected int $eccLevel = QRCode::ECC_L;
 
 	/**
 	 * Mask Pattern to use
 	 *
-	 *   [0...7] or QRCode::MASK_PATTERN_AUTO
+	 * [0...7] or QRCode::MASK_PATTERN_AUTO
 	 */
 	protected int $maskPattern = QRCode::MASK_PATTERN_AUTO;
 
@@ -59,12 +65,13 @@ trait QROptionsTrait{
 	/**
 	 * Size of the quiet zone
 	 *
-	 *   internally clamped to [0 ... $moduleCount / 2], defaults to 4 modules
+	 * internally clamped to [0 ... $moduleCount / 2], defaults to 4 modules
 	 */
 	protected int $quietzoneSize = 4;
 
 	/**
 	 * Use this to circumvent the data mode detection and force the usage of the given mode.
+	 *
 	 * valid modes are: Number, AlphaNum, Kanji, Byte
 	 *
 	 * @see https://github.com/chillerlan/php-qrcode/issues/39
@@ -72,10 +79,12 @@ trait QROptionsTrait{
 	protected ?string $dataMode = null;
 
 	/**
-	 * QRCode::OUTPUT_MARKUP_XXXX where XXXX = HTML, SVG
-	 * QRCode::OUTPUT_IMAGE_XXX where XXX = PNG, GIF, JPG
-	 * QRCode::OUTPUT_STRING_XXXX where XXXX = TEXT, JSON
-	 * QRCode::OUTPUT_CUSTOM
+	 * The output type
+	 *
+	 *   - QRCode::OUTPUT_MARKUP_XXXX where XXXX = HTML, SVG
+	 *   - QRCode::OUTPUT_IMAGE_XXX where XXX = PNG, GIF, JPG
+	 *   - QRCode::OUTPUT_STRING_XXXX where XXXX = TEXT, JSON
+	 *   - QRCode::OUTPUT_CUSTOM
 	 */
 	protected string $outputType = QRCode::OUTPUT_IMAGE_PNG;
 
@@ -95,8 +104,7 @@ trait QROptionsTrait{
 	protected string $eol = PHP_EOL;
 
 	/**
-	 * size of a QR code pixel [SVG, IMAGE_*]
-	 * HTML -> via CSS
+	 * size of a QR code pixel [SVG, IMAGE_*], HTML via CSS
 	 */
 	protected int $scale = 5;
 
@@ -190,8 +198,8 @@ trait QROptionsTrait{
 	/**
 	 * Module values map
 	 *
-	 *   HTML, IMAGICK: #ABCDEF, cssname, rgb(), rgba()...
-	 *   IMAGE: [63, 127, 255] // R, G, B
+	 *   - HTML, IMAGICK: #ABCDEF, cssname, rgb(), rgba()...
+	 *   - IMAGE: [63, 127, 255] // R, G, B
 	 */
 	protected ?array $moduleValues = null;