It does throw an exception in hogan.js:

```js
Hogan = require("hogan.js");

var template = "{{< foo }}{{# bar }}{{$ baz }}{{/ baz }}{{/ bar }}{{/ foo }}";

var foo = "{{$baz}}default content{{/baz}}";

var data = {
    bar: "set by user"
}

var template = Hogan.compile(template);
var output = template.render(data, {'foo': header});

console.log(output);
// Returns
/*
 * /home/dmiller/development/test.js/node_modules/hogan.js/lib/compiler.js:203
 *       throw new Error('Illegal content in < super tag.');
 *                     ^
 *                     Error: Illegal content in < super tag.
 *                         at buildTree (/home/dmiller/development/test.js/node_modules/hogan.js/lib/compiler.js:203:15)
 *       at buildTree (/home/dmiller/development/test.js/node_modules/hogan.js/lib/compiler.js:208:23)
 *       at Object.Hogan.parse (/home/dmiller/development/test.js/node_modules/hogan.js/lib/compiler.js:394:12)
 *       at Object.Hogan.compile (/home/dmiller/development/test.js/node_modules/hogan.js/lib/compiler.js:416:35)
 *       at Object.<anonymous> (/home/dmiller/development/test.js/index.js:11:22)
 *       at Module._compile (module.js:456:26)
 *       at Object.Module._extensions..js (module.js:474:10)
 *       at Module.load (module.js:356:32)
 *       at Function.Module._load (module.js:312:12)
 *       at Function.Module.runMain (module.js:497:10)
 */
```

I'll add a throw here for that.