Let's consider the following plunk:

http://plnkr.co/edit/pPQWTgkzTLyBdBIX8vfQ?p=preview

MyItemCtrl.js

var klass = require("hsp/klass");

var MyItemCtrl= klass({
    attributes: {
        "foo" : { type : "string"},
        "bar" : { type : "string" }
    }
});

module.exports = MyItemCtrl;

hello.hsp

var MyItemCtrl = require("./MyItemCtrl");

{template Hello}
  <#myItem foo="FOO" bar="BAR" />
{/template}

{template myItem using ctrl:MyItemCtrl}
  foo = {ctrl.foo} <br>
  bar = {ctrl.bar} <br>
{/template}

module.exports = Hello;

So far so good, I define attributes in the controller (foo and bar) and pass them from Hello template to <#myItem> and everything works properly.

Now, let's change line 4 in hello.hsp from:

<#myItem foo="FOO" bar="BAR" /> 

to

<#myItem foo="FOO" bar="BAR" xxx="xxx" />

i.e. let's pass some redundant attrib that is not defined in attributes of the controller.

What we get is a compilation failure plus a cryptic error message:

TypeError: this.ctlAttributes[nm] is undefined
if (this.ctlAttributes[nm].type !== "template") {

I think the code should still compile fine, only raising a warning, with a better description of the issue.