<p>To be specific, here is the permalink to the relevant line of code: <a href="https://github.com/istio/istio/blob/e3a376610c2f28aef40296aac722c587629123c1/install/kubernetes/helm/istio/templates/sidecar-injector-configmap.yaml#L84" rel="nofollow noreferrer">https://github.com/istio/istio/blob/e3a376610c2f28aef40296aac722c587629123c1/install/kubernetes/helm/istio/templates/sidecar-injector-configmap.yaml#L84</a></p>

<blockquote>
  <p>{{ "[[ .ProxyConfig.ZipkinAddress ]]" }}</p>
</blockquote>

<p>The <code>[[</code> and <code>]]</code> seems alien to me, and in the helm chart developer guide doc <a href="https://docs.helm.sh/chart_template_guide/#the-chart-template-developer-s-guide" rel="nofollow noreferrer">here</a>, it doesn't show any example or documentation about <code>[[</code> and <code>]]</code> syntax. </p>

<p>Also, when I tried to render my istio installation (using <code>helm template</code> command), the <code>{{ "[[ .ProxyConfig.ZipkinAddress ]]" }}</code> part only rendered as <code>[[ .ProxyConfig.ZipkinAddress ]]</code>. So I guess that <code>[[</code> and <code>]]</code> is not part of helm template syntax. My guess it would be internal istio's related syntax, which I don't know what exactly it is.</p>

<p>Any idea?</p>

<p>I got the answer after posting the same question on the Istio's google group <a href="https://groups.google.com/forum/#!topic/istio-users/0dfU_y06n1Q" rel="nofollow noreferrer">here</a>. Without discrediting the author who answering me in the google group, the answer is yes it is a template of a template. The template syntax is used by sidecar injection described in here: <a href="https://istio.io/docs/setup/kubernetes/sidecar-injection/#template" rel="nofollow noreferrer">https://istio.io/docs/setup/kubernetes/sidecar-injection/#template</a></p>
