Use the form mixin in any form

from django import forms
from dj_warning_forms.forms import WarningFormMixin, FormFieldWarning

from .models import Poll


class PollForm(WarningFormMixin, forms.ModelForm):
    question = forms.CharField(
        max_length=200, widget=forms.TextInput(attrs={"autocomplete": "off"})
    )

    class Meta:
        model = Poll
        fields = "__all__"

    def warning_question(self) -> List[FormFieldWarning]:
        if not self.cleaned_data["question"].endswith("?"):
            return [
                FormFieldWarning(
                    message="Weird question",
                    description="This question does not end with a question mark. Are you sure you want to publish this question?",  # noqa
                )
            ]
        return []

Adding a warning is as simple as adding a method with the warning_ prefix. This method must return a list of FormFieldWarning objects.

Showing warnings in the template

You can find the list of warnings in form.warnings.

{% block content %}
<form action="." method="post">
    {% csrf_token %}
    {{ form }}
    <input type="submit" value="Submit">

    <!-- Customize your form warnings as you wish -->
    {% if form.warnings %}
        <div class="rounded p-2 mt-2 bg-warning">
            <ul>
            {% for warning in form.warnings %}
                <li><b>{{ warning.message }}:</b> {{ warning.description }}</li>
            {% endfor %}
            </ul>
        </div>
    {% endif %}
    <!-- End of form warnings -->
</form>
{% endblock %}