add element domain

backend/app/Element/Element.php

@@ -0,0 +1,47 @@
+<?php
+
+namespace App\Element;
+
+use App\Set\Set;
+
+final readonly class Element
+{
+    public function __construct(
+        private int $id,
+        private string $name,
+        private string $kind,
+        private Set $set,
+        private ?Element $parentElement,
+        private int $position,
+    ) {}
+
+    public function getId(): int
+    {
+        return $this->id;
+    }
+
+    public function getName(): string
+    {
+        return $this->name;
+    }
+
+    public function getKind(): string
+    {
+        return $this->kind;
+    }
+
+    public function getSet(): Set
+    {
+        return $this->set;
+    }
+
+    public function getParentElement(): ?Element
+    {
+        return $this->parentElement;
+    }
+
+    public function getPosition(): int
+    {
+        return $this->position;
+    }
+}