Twig (Symfony2) doesn't see variable in 'extend' block
===

I define variable in controller and pass it to template but it's not visible in `extend` block. The important controller code is:

			$response['html'] = $this->renderView(
				'AldenXyzBundle:Profile:edit_ajax.html.twig', array(
					'isXmlHttpRequest' => $request->isXmlHttpRequest(),
				)
			);
and Twig template

	{% extends isXmlHttpRequest ? '::base-ajax.html.twig' : '::base.html.twig' %}

	{% block content %}
	...
	{% endblock %}
and I have exception `Variable "isXmlHttpRequest" does not exist in ...` while the template

	{% extends '::base-ajax.html.twig' %}

	{% block content %}
	{{ dump(isXmlHttpRequest) }}
	...
	{% endblock %}
works well and display correct `$isXmlHttpRequest` value.

I also tried directly in template:

	{% extends app.request.isXmlHttpRequest ? '::base-ajax.html.twig' : '::base.html.twig' %}

but I got an exception saying app is undefined.