[FormatInterface] Implement functions in the template

FormatInterface.md

@@ -91,6 +91,10 @@ This is a bare minimum template for a format:
 ```PHP
 <?php
 class MyTypeFormat implements FormatInterface {
+    private $items;
+    private $charset;
+    private $extraInfos;
+
     public function stringify(){
         // Implement your code here
         return ''; // Return items as string
@@ -103,33 +107,30 @@ class MyTypeFormat implements FormatInterface {
     }
 
     public function setItems(array $items){
-        // Implement your code here!
+        $this->items = $items;
         return $this;
     }
 
     public function getItems(){
-        // Implement your code here!
-        return array(); // Return original items
+        return $this->items;
     }
 
     public function setCharset($charset){
-        // Implement your code here!
+        $this->charset = $charset;
         return $this;
     }
 
     public function getCharset(){
-        // Implement your code here!
-        return ''; // Return the charset!
+        return $this->charset;
     }
 
     public function setExtraInfos(array $infos){
-        // Implement your code here!
+        $this->extraInfos = $infos;
         return $this;
     }
 
     public function getExtraInfos(){
-        // Implement your code here!
-        return array(); // Return the original infos!
+        return $this->extraInfos;
     }
 }
 // Imaginary empty line!