We should be able to define an attribute with no value

Ex : "itemscope" to generate breadcrumb with microdatas for SEO:

```html
<ul class="list-inline breadcrumb">
<li  itemscope itemtype="http://data-vocabulary.org/Breadcrumb" class="first"> <a href="/">Homepage</a></li>
<li  itemscope itemtype="http://data-vocabulary.org/Breadcrumb" class="last"> <a href="/architects">Architects</a></li>
</ul>
```
Ok, I didn't know the "none" syntax.