Where can I find traceur options

Question

I keep getting exceptions while using es6ify and browserify. This is my gulp code:

es6ify.traceurOverrides = {
    asyncFunctions: true,
    freeVariableChecker: true
};

browserify(params)
    .add(es6ify.runtime)
    .transform(es6ify)
    .require(require.resolve('app/index.js'), { entry: true })
    .bundle()
    ...
    ...

First, I got an error regarding a file that contained:

import a, { func } from 'some/module';

The exception was:

Unexpected token , while parsing file: <file path>

For some reason this was solved when I set freeVariableChecker to true. Now I get an error:

window is not defined while parsing file: <file path>

And I don't understand which option should fix this issue.

Any idea where I can find explanations on traceur options?
Any idea how to solve this issue?

Thanks