Explanation of the ingress controller annotation in Lab 10.1

bryonbaker

Hi,
I am trying to understand the annotation used in Lab 10.1.
The documentation on Traefik's website states:

Value of kubernetes.io/ingress.class annotation that identifies Ingress objects to be processed.
If the parameter is non-empty, only Ingresses containing an annotation with the same value are processed.
Otherwise, Ingresses missing the annotation, having an empty value, or the value traefik are processed.

What I am struggling with is finding where and how the annotation "traefik" is used as it does not appear in any other YAML file. Could you please explain where and how this annotation is used?
Thanks