Let's say you have a file named bar.j2 in your templates directory.

/etc/ansible/roles/foo/templates/bar.j2

And let's say bar.j2 contains the following.

{%Y}

Since templates are part of roles, lets say you have a playbook that invokes the foo role.

---
- hosts: all
  roles:
    - role: foo

And let's say /etc/ansible/roles/foo/tasks/main.yml contains the following.

- name: copy ipv4.j2 to /tmp/ipv4.conf
  template:
    src: ipv4.j2
    dest: /tmp/ipv4.conf

Running this play would return Encounted unknown tag 'Y' because {%Y} is built in jinja2 syntax.

Encounted unknown tag 'Y'

In this scenario, {% raw %} and {% endraw %} are wrapped around the {%Y} built in jinja2 syntax so that {%Y} is not interpreted as jinja2.

{% raw %}{%Y}{% endraw %}