diff --git a/src/MinifyCSS.php b/src/MinifyCSS.php
index 947de8e..d63f892 100644
--- a/src/MinifyCSS.php
+++ b/src/MinifyCSS.php
@@ -6,19 +6,44 @@
 
 use MatthiasMullie\Minify;
 
+/**
+ * [Description MinifyCSS].
+ */
 class MinifyCSS extends ShrinkWrap {
+    /**
+     * @var array
+     */
     private $available_engines = ['matthiasmullie', 'regex'];
 
+    /**
+     * @var string
+     */
     private $engine;
+
+    /**
+     * @var array
+     */
     private $options;
 
+    /**
+     * @var mixed
+     */
     private $minifier;
 
+    /**
+     * @param string $engine
+     * @param array  $options
+     */
     public function __construct(string $engine = 'matthiasmullie', array $options = []) {
         in_array($engine, $this->available_engines) ? $this->engine = $engine : $this->engine = 'matthiasmullie';
         $this->options = $options;
     }
 
+    /**
+     * @param null|string $data
+     *
+     * @return null|mixed
+     */
     public function init(string $data = null) {
         switch ($this->engine) {
             case 'matthiasmullie':
@@ -28,6 +53,11 @@ public function init(string $data = null) {
         }
     }
 
+    /**
+     * @param null|string $data
+     *
+     * @return null|mixed
+     */
     public function minify(string $data = null) {
         switch ($this->engine) {
             case 'matthiasmullie':
@@ -35,6 +65,11 @@ public function minify(string $data = null) {
         }
     }
 
+    /**
+     * @param string $data
+     *
+     * @return null|mixed
+     */
     public function add(string $data) {
         switch ($this->engine) {
             case 'matthiasmullie':
diff --git a/src/MinifyHTML.php b/src/MinifyHTML.php
index 7602536..dca9812 100644
--- a/src/MinifyHTML.php
+++ b/src/MinifyHTML.php
@@ -6,14 +6,33 @@
 
 use voku\helper\HtmlMin;
 
+/**
+ * [Description MinifyHTML].
+ */
 class MinifyHTML extends ShrinkWrap {
+    /**
+     * @var array
+     */
     private $available_engines = ['voku', 'regex'];
 
+    /**
+     * @var string
+     */
     private $engine;
+
+    /**
+     * @var array
+     */
     private $options;
 
+    /**
+     * @var mixed
+     */
     private $minifier;
 
+    /**
+     * @var array
+     */
     private $voku_options = [
         'doOptimizeViaHtmlDomParser'                   => false, // optimize html via "HtmlDomParser()"
         'doRemoveComments'                             => false, // remove default HTML comments (depends on "doOptimizeViaHtmlDomParser(true)")
@@ -41,11 +60,20 @@ class MinifyHTML extends ShrinkWrap {
         'doRemoveOmittedHtmlTags'                      => false, // remove ommitted html tags e.g. <p>lall</p> => <p>lall
     ];
 
+    /**
+     * @param string $engine
+     * @param array  $options
+     */
     public function __construct(string $engine = 'voku', array $options = []) {
         in_array($engine, $this->available_engines) ? $this->engine = $engine : $this->engine = 'voku';
         $this->options = $options;
     }
 
+    /**
+     * @param null|string $data
+     *
+     * @return null|mixed
+     */
     public function init(string $data = null) {
         switch ($this->engine) {
             case 'voku':
@@ -62,6 +90,11 @@ public function init(string $data = null) {
         }
     }
 
+    /**
+     * @param null|string $data
+     *
+     * @return null|mixed
+     */
     public function minify(string $data = null) {
         switch ($this->engine) {
             case 'voku':
diff --git a/src/MinifyJS.php b/src/MinifyJS.php
index 8ad3047..bf2d21e 100644
--- a/src/MinifyJS.php
+++ b/src/MinifyJS.php
@@ -6,19 +6,44 @@
 
 use MatthiasMullie\Minify;
 
+/**
+ * [Description MinifyJS].
+ */
 class MinifyJS extends ShrinkWrap {
+    /**
+     * @var array
+     */
     private $available_engines = ['matthiasmullie', 'regex'];
 
+    /**
+     * @var string
+     */
     private $engine;
+
+    /**
+     * @var array
+     */
     private $options;
 
+    /**
+     * @var mixed
+     */
     private $minifier;
 
+    /**
+     * @param string $engine
+     * @param array  $options
+     */
     public function __construct(string $engine = 'matthiasmullie', array $options = []) {
         in_array($engine, $this->available_engines) ? $this->engine = $engine : $this->engine = 'matthiasmullie';
         $this->options = $options;
     }
 
+    /**
+     * @param null|string $data
+     *
+     * @return null|mixed
+     */
     public function init(string $data = null) {
         switch ($this->engine) {
             case 'matthiasmullie':
@@ -28,6 +53,11 @@ public function init(string $data = null) {
         }
     }
 
+    /**
+     * @param null|string $data
+     *
+     * @return null|mixed
+     */
     public function minify(string $data = null) {
         switch ($this->engine) {
             case 'matthiasmullie':
@@ -35,6 +65,11 @@ public function minify(string $data = null) {
         }
     }
 
+    /**
+     * @param string $data
+     *
+     * @return null|mixed
+     */
     public function add(string $data) {
         switch ($this->engine) {
             case 'matthiasmullie':
diff --git a/src/ShrinkWrap.php b/src/ShrinkWrap.php
index 0d789cb..ec6479d 100644
--- a/src/ShrinkWrap.php
+++ b/src/ShrinkWrap.php
@@ -98,6 +98,10 @@ public function __construct() {
         $this->domparser = new HTML5();
     }
 
+    /**
+     * @param mixed $method
+     * @param mixed $args
+     */
     public function __call($method, $args) {
         echo "Calling unknown object method '{$method}' " . json_encode($args) . "\n";
     }