Explanation of vocabularies seems confusing.

The explanation of vocabularies seems confusing. There's more than one attempt to explain them, so let's read the one here:

http://doc.nuxeo.com/display/Studio/Add+a+new+vocabulary

I have to admit, I still don't understand how those three types of vocabularies relate to one another. At first, I thought a simple vocabulary was just that, simple, only one level. Further down, though, it seems that a simple vocabulary can have children. Also, the hierarchical vocabulary seems defined as having two levels, which seems odd, since there's another page that explains vocabularies here:

http://doc.nuxeo.com/display/DMDOC/Manage+vocabularies

which defines a hierarchical vocabulary as potentially having "several" levels. It would help if there was a single page that explained this, particularly with an example or two to drive home the description.