How to use/populate template twig variables?

I’m in the process of creating a template. I found a couple of variables in the built-in *.twig.html files, but I don’t find any information about them in the docs.

Let’s take the Coffee template as an example. It comes with form.html.twig. The file contains:

{% extends ":coffee:base.html.twig" %}

{% block content %}
    {% if message is defined %}
        <div class="well text-center">
            <p>{{ message|raw }}</p>
    {% endif %}

    <div class="form-container">
        {% if header is defined %}
        <h4>{{ header }}</h4>
        {% endif %}
        {{ content|raw }}
{% endblock %}
  • content is the actual form, which is created via the compoents → form builder.
  • What is message? It’s not the response message after the form was submitted. This data/string gets populated into <div class="mauticform-message" id="mauticform_FORMID_message">MESSAGE.</div>
  • What is header? How do I define it?

I could especially use header, because I’d like to define a header that gets shown if the form is standalone (, but it won’t get shown if the form is embedded in a landing page ( with the slot {form=ID}.

Can header be used for this? How so?