title: What is LeftNav in material-ui?
body: <p>I keep seeing references to a component called "<code>LeftNav</code>" in the material-ui react library (example: <a href="https://stackoverflow.com/questions/28691964/material-ui-open-leftnav-on-appbar-click">Material UI - Open LeftNav / Drawer on AppBar click</a>), but I can't find anything about it in the documentation.  What is it?  How does it differ from <code>Drawer</code>?  Why is it apparently undocumented, despite being hugely popular (at least judging by the number of questions I see about how to use it)?  What is its <code>toggle()</code> method for, and is there a similar method for <code>Drawer</code> (the documentation suggests not, but for all I would know by reading the documentation there was no such component as <code>LeftNav</code> at all, so I don't think the documentation can really be trusted here)?</p>