tmux pane-activity indicator behavior with concurrent pane activity

tmux supports pane-activity monitoring via the monitor-activity and visual-activity client options, which set a pane-activity flag when a pane receives new output and can display an indicator in the status line.

The documented behavior of the flag and the visual indicator is ambiguous under concurrent activity. The documentation does not explicitly state whether pane-activity is triggered only by new output or also by key presses, how the indicator is prioritized when multiple panes become active at the same time, and whether viewing a pane automatically clears the flag. Behavior may vary between tmux 3.1, 3.2 and 3.3, and visual-activity can be suppressed when the pane is active or when mouse mode is enabled.

tmux does not provide a documented command to clear the pane-activity flag programmatically, which makes the expected reset semantics unclear.

Does pane-activity get set only on new output or also on key presses? How is the visual-activity indicator presented when multiple panes generate activity simultaneously? Does viewing a pane automatically clear the pane-activity flag in tmux 3.1 to 3.3?