Add more documentation for the Attribute node.

Author: drupol

src/Exporter/Ascii.php

@@ -58,7 +58,7 @@ public function export(NodeInterface $node): string
     protected function getNodeRepresentation(NodeInterface $node): string
     {
         if ($node instanceof ValueNodeInterface) {
-            return $node->getValue();
+            return (string) $node->getValue();
         }
 
         return \sha1(\spl_object_hash($node));

src/Node/AttributeNode.php

@@ -33,7 +33,7 @@ public function __construct(
     /**
      * {@inheritdoc}
      */
-    public function getAttribute($key)
+    public function getAttribute(string $key)
     {
         return $this->getAttributes()[$key] ?? null;
     }

src/Node/AttributeNodeInterface.php

@@ -10,22 +10,42 @@
 interface AttributeNodeInterface extends NaryNodeInterface
 {
     /**
-     * {@inheritdoc}
+     * Get an attribute.
+     *
+     * @return mixed
+     *   The value of the attribute.
      */
-    public function getAttribute($key);
+    public function getAttribute(string $key);
 
     /**
-     * {@inheritdoc}
+     * Get the attributes.
+     *
+     * @return \Traversable
+     *   The attributes.
      */
     public function getAttributes(): \Traversable;
 
     /**
-     * {@inheritdoc}
+     * Set an attribute.
+     *
+     * @param string $key
+     *   The attribute key.
+     * @param mixed $value
+     *   The attribute value.
+     *
+     * @return \drupol\phptree\Node\AttributeNodeInterface
+     *   The node.
      */
     public function setAttribute(string $key, $value): AttributeNodeInterface;
 
     /**
-     * {@inheritdoc}
+     * Set the attributes.
+     *
+     * @param \Traversable $attributes
+     *   The attributes.
+     *
+     * @return \drupol\phptree\Node\AttributeNodeInterface
+     *   The node.
      */
     public function setAttributes(\Traversable $attributes): AttributeNodeInterface;
 }