feat(docs): sidebar, table of contents, highlights list

docs/User Guide/User Guide/Basic Concepts and Features/UI Elements/Right Sidebar.md

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+# Right Sidebar
+<figure class="image"><img style="aspect-ratio:1036/372;" src="Right Sidebar_image.png" width="1036" height="372"></figure>
+
+The right sidebar displays specific content for the current note. Currently it includes:
+
+*   <a class="reference-link" href="../../Note%20Types/Text/Table%20of%20contents.md">Table of contents</a>
+*   <a class="reference-link" href="../../Note%20Types/Text/Highlights%20list.md">Highlights list</a>
+
+Note that the sidebar is not displayed if it would otherwise be empty, for example if there are too few headings and there are no highlights.
+
+## Toggling the right sidebar
+
+The sidebar can be hidden or shown by using the `toggleRightPane` keyboard shortcut, which is not assigned by default.
+
+## Relation with splits
+
+When using <a class="reference-link" href="Split%20View.md">Split View</a>, there is a single sidebar serving all the open splits for the current [tab](Tabs.md).
+
+Clicking on a note within the split view will display the sidebar for that note. If there are no items to display in the sidebar, it will remain closed.