Added the ability to add child elements to the element

src/DiDom/Element.php

@@ -3,6 +3,7 @@
 namespace DiDom;
 
 use DOMDocument;
+use DOMElement;
 use InvalidArgumentException;
 
 class Element
@@ -39,6 +40,37 @@ public function __construct($name, $value = '', $attributes = [])
         }
     }
 
+    /**
+     * Adds new child at the end of the children.
+     * 
+     * @param  \DiDom\Element|\DOMElement|array $nodes The appended child.
+     *
+     * @return \DiDom\Element
+     *
+     * @throws \InvalidArgumentException if the provided argument is not an instance of \DOMElement or \DiDom\Element
+     */
+    public function appendChild($nodes)
+    {
+        $nodes = is_array($nodes) ? $nodes : [$nodes];
+
+        foreach ($nodes as $node) {
+            if ($node instanceof Element) {
+                $node = $node->getNode();
+            }
+
+            if (!$node instanceof DOMElement) {
+                throw new InvalidArgumentException(sprintf('Argument 1 passed to %s must be an instance of %s\Element or DOMElement, %s given', __METHOD__, __NAMESPACE__, (is_object($node) ? get_class($node) : gettype($node))));
+            }
+
+            $cloned = $node->cloneNode(true);
+            $newNode = $this->node->ownerDocument->importNode($cloned, true);
+
+            $this->node->appendChild($newNode);
+        }
+
+        return $this;
+    }
+
     /**
      * Checks the existence of the item.
      * 

tests/DiDom/ElementTest.php

@@ -35,6 +35,36 @@ public function testCreateFromDomElement()
         $this->assertEquals($node, $element->getNode());
     }
 
+    /**
+     * @expectedException InvalidArgumentException
+     */
+    public function testAppendChildWithInvalidArgument()
+    {
+        $element = new Element('span', 'hello');
+
+        $element->appendChild('foo');
+    }
+
+    public function testAppendChild()
+    {
+        $list = new Element('ul');
+
+        $this->assertCount(0, $list->find('li'));
+
+        $node = new Element('li', 'foo');
+        $list->appendChild($node);
+
+        $this->assertCount(1, $list->find('li'));
+
+        $items = [];
+        $items[] = new Element('li', 'bar');
+        $items[] = new Element('li', 'baz');
+
+        $list->appendChild($items);
+
+        $this->assertCount(3, $list->find('li'));
+    }
+
     public function testHas()
     {
         $document = new \DOMDocument();