Jinja.jinja

1. Jinja Macros can return results (but only if `called`):

```
{% macro foo() %}
  hello from foo
  {{ caller({"bar":1}) if caller is defined }}
{% endmacro %}

{% call(result) foo() %}
  {{result.bar}}
{% endcall %}
```

Output is: 

  hello from foo 1

2. Macros can take varargs and kwargs (but only if you use them in the macro body):

```
{% macro baz() %}
  hello from baz {{varargs}} {{kwargs}}
{% endmacro %}

{% set args = [1,2,3] %}
{% set kwargs = {"qux": 1} %}
{{ baz(*args, **kwargs) }}
```

Output is: 

  hello from baz (1, 2, 3) {'qux': 1}

If you don't want to render them, but still allow them:

```
{% macro baz() %}
  {% if false %}{{varargs}} {{kwargs}} {% endif %}
  hello from baz
{% endmacro %}
```

Output is:

  hello from baz

Or, succinctly:

```
{% macro baz() %}
  {{kwargs and varargs if 0}}
  hello from baz
{% endmacro %}
```

3. Macros can set variables outside their scope, but only if namespaced:

This won't work:

{% macro zod(x) %}  {# with or without passing x #}
  {% set x = x + 1%}
{% endmacro %}

{% set x = 1%}
{{zod(x)}}
{{x}}

But this will:

{% macro zed(ns) %}  {# with or without passing ns #}
  {% set ns.x = ns.x + 1%}
{% endmacro %}

{% set ns = namespace(x=1) %}
{{zed(ns)}}
{{ns.x}}

4. extended Set:

{% set name = "bar" %}

{% set foo | safe %}
<input type="text" name="{{bar}}">
{% endset %}

{{foo}} {# output is <input type="text" name="bar"> #}

5. callbacks:

{% macro foo(save_clicked=none) %}  {# where save_clicked can be a macro or python function #}
  {% if "save" in request.form %}
    {{ save_clicked(...) if save_clicked is callable %}
  {% endif %}
{% endmacro %}