diff --git a/src/Bindable.php b/src/Bindable.php
index 377fed2..e76d8bb 100644
--- a/src/Bindable.php
+++ b/src/Bindable.php
@@ -79,11 +79,8 @@ protected function setData(BaseElement $element, iterable $data):void {
 				continue;
 			}
 
-			$key = $this->getKeyFromAttribute($element, $attr);
-			if(!isset($data[$key])) {
-				throw new BoundDataNotSetException($key);
-			}
-			$dataValue = $data[$key];
+			$dataKeyMatch = $this->getKeyFromAttribute($element, $attr);
+			$dataValue = $dataKeyMatch->getValue($data) ?? "";
 
 			switch($matches[1]) {
 			case "html":
@@ -104,9 +101,15 @@ protected function setData(BaseElement $element, iterable $data):void {
 		}
 	}
 
-	protected function getKeyFromAttribute(BaseElement $element, Attr $attr):string {
+	protected function getKeyFromAttribute(BaseElement $element, Attr $attr):DataKeyMatch {
+		$required = true;
 		$key = $attr->value;
 
+		if($key[0] === "?") {
+			$required = false;
+			$key = substr($key, 1);
+		}
+
 		if($key[0] === "@") {
 			$key = substr($key, 1);
 			$attributeValue = $element->getAttribute($key);
@@ -114,10 +117,10 @@ protected function getKeyFromAttribute(BaseElement $element, Attr $attr):string
 				throw new BoundAttributeDoesNotExistException($attr->name);
 			}
 
-			return $attributeValue;
+			$key = $attributeValue;
 		}
 
-		return $key;
+		return new DataKeyMatch($key, $required);
 	}
 
 	protected function wrapData(iterable $data):iterable {
diff --git a/src/DataKeyMatch.php b/src/DataKeyMatch.php
new file mode 100644
index 0000000..ecf7b86
--- /dev/null
+++ b/src/DataKeyMatch.php
@@ -0,0 +1,24 @@
+<?php
+namespace Gt\DomTemplate;
+
+class DataKeyMatch {
+	public function __construct(string $key, bool $required) {
+		$this->key = $key;
+		$this->required = $required;
+	}
+
+	public function checkDataExists(iterable $data) {
+		if(!$this->required) {
+			return;
+		}
+
+		if(!isset($data[$this->key])) {
+			throw new BoundDataNotSetException($this->key);
+		}
+	}
+
+	public function getValue(iterable $data):?string {
+		$this->checkDataExists($data);
+		return $data[$this->key] ?? null;
+	}
+}
\ No newline at end of file
diff --git a/test/unit/BindableTest.php b/test/unit/BindableTest.php
index 42f12dc..3bc2995 100644
--- a/test/unit/BindableTest.php
+++ b/test/unit/BindableTest.php
@@ -1,6 +1,7 @@
 <?php
 namespace Gt\DomTemplate\Test;
 
+use Gt\DomTemplate\BoundDataNotSetException;
 use Gt\DomTemplate\HTMLDocument;
 use Gt\DomTemplate\Test\Helper\Helper;
 use PHPUnit\Framework\TestCase;
@@ -185,4 +186,41 @@ public function testBindWithInlineNamedTemplateWhenAnotherTemplateExists() {
 		self::assertContains("Implement features", $todoListElement->innerHTML);
 		self::assertNotContains("Use the other template instead!", $todoListElement->innerHTML);
 	}
+
+	public function testBindWithNonOptionalKey() {
+		$document = new HTMLDocument(Helper::HTML_TODO_LIST);
+		$todoData = [
+			["title" => "Write tests", "complete" => true],
+			["title" => "Implement features", "complete" => false],
+			["title" => "Pass tests", "complete" => false],
+		];
+		$document->extractTemplates();
+		$todoListElement = $document->getElementById("todo-list");
+
+		self::expectException(BoundDataNotSetException::class);
+		$todoListElement->bind($todoData);
+	}
+
+	public function testBindWithOptionalKey() {
+		$document = new HTMLDocument(Helper::HTML_TODO_LIST_OPTIONAL_ID);
+		$todoData = [
+			["title" => "Write tests", "complete" => true],
+			["title" => "Implement features", "complete" => false],
+			["title" => "Pass tests", "complete" => false],
+		];
+		$document->extractTemplates();
+		$todoListElement = $document->getElementById("todo-list");
+
+		$todoListElement->bind($todoData);
+		$items = $todoListElement->querySelectorAll("li");
+		self::assertCount(3, $items);
+
+		self::assertEquals(
+			"Implement features",
+			$items[1]->querySelector("input[name=title]")->value
+		);
+		self::assertNull(
+			$items[1]->querySelector("input[name=id]")->value
+		);
+	}
 }
\ No newline at end of file
diff --git a/test/unit/Helper/Helper.php b/test/unit/Helper/Helper.php
index c4877b6..908f94e 100644
--- a/test/unit/Helper/Helper.php
+++ b/test/unit/Helper/Helper.php
@@ -188,5 +188,35 @@ class Helper {
 		</li>
 	</ul>
 </main>
+HTML;
+
+	const HTML_TODO_LIST_OPTIONAL_ID = <<<HTML
+<!doctype html>
+<meta charset="utf-8" />
+<title>Todo list</title>
+<main>
+	<ul id="todo-list">
+		<li data-template>
+			<input name="id" data-bind:value="?id" />
+			<input name="title" data-bind:value="@name" />
+			<button name="do" value="complete">Complete</button>		
+		</li>
+	</ul>
+</main>
+HTML;
+
+	const HTML_TODO_LIST_OPTIONAL_ID_REFERENCED = <<<HTML
+<!doctype html>
+<meta charset="utf-8" />
+<title>Todo list</title>
+<main>
+	<ul id="todo-list">
+		<li data-template>
+			<input name="id" data-bind:value="?@name" />
+			<input name="title" data-bind:value="@name" />
+			<button name="do" value="complete">Complete</button>		
+		</li>
+	</ul>
+</main>
 HTML;
 }
\ No newline at end of file