Collapsible track groups in the Keyframe Editor - tracks sit under group
headers: muscle groups for humanoid rigs, bone groups for generic ones. A
collapsed group shows all of its child keys as one aggregated summary row.
Group interactions - click a header to collapse or expand it, Alt-click for
every group at once, right-click a group row in the dopesheet to add keyframes
to that group only. The collapse state survives across sessions.
Track show filters in the visibility menu: Only Animated and Only Keyed
at Playhead, which updates live while scrubbing. A Show Groups toggle
turns grouping off entirely.
An Events header row above the track list - mute and unmute audio events
and collapse or expand all groups from one place.
A play/pause button on the Single Clip control bar.