I may be misunderstanding how to use it, as i only see there is the ability to pin it above the demo tiddler…
EDIT: oh I see, onHover of the icons on the far right will show different modals such as the cotrol panel and slidebar demo, and clicking the icons swap them out.
I think it’s a nice UI feature, but I don’t believe I have a usecase for this, so it would be wasted on me. I will say once I figured out what was going on, I did like the idea of togglable sidebars, it reminds me of earlier plans I made for making a desktop and mobile theme, where the bottom toolbar in mobile (like the one seen in JD’s mobile plugin) would be the same as the toolbar present on the left/right side of the tiddler in desktop view.
Anyhow, I’m getting off topic. I think it could prove useful for users looking for that sort of functionality 
. . .
(For SidebarSlider Plugin)
Oh also! I noticed that when used on the left side with a palette that shows the divider to tabs, the divider border, wiki title, and other elements* will go through the slider’s divider.
i threw together this conditional stylesheet that resolves this, but I’m not sure if it would need to be optimized better or not.
$__themes_tiddlywiki_vanilla_metrics_sidebar-tab-divider-width.json (798 Bytes)