Thot Metadata
Every thot has optional thot metadata, a set of optional metadata items assignable to each thot, including a File, a Cover Image, Note References, Piles, Whispers, Inklings, and Palette Images.
A thot's metadata is always visible on the root thot, but for all other thots, the thot metadata must be toggled on to see it by pressing the action on the toolbar.
When thot metadata is toggled on, only the root thot and active thot will reveal their metadata items, but you can quickly spot which thots have metadata items assigned by looking for a thin gray line to the right of the editor's thots.
Even though note references are not considered a "thot metadata item", being able to insert a note reference into a thot's text content from the toolbar requires toggling metadata on by pressing the action on the toolbar.