Attributes are the free-form, per-knot metadata stored in the attributes hstore column. A handful of names recur often enough across templates to be worth knowing: template (which .tt file should render this knot), public (whether anonymous visitors may see it), creator and epoch (who made it and when), img_url (an illustration), ogg_url and presentation_timeline (audio narration and its synced slide-navigation events, used by mainframe), and voice/age/gender/motherlang/consent (speaker metadata for recordings).

Because attributes is schemaless, nothing stops a template from inventing its own attribute name for its own purposes -- these are simply the ones already in wide use across the existing templates.