The Selection page appears in the Adjust Events property window, when invoked by a command from the Track menu.  The caption of the window depends on the type of adjustment.

It allows you to select the range of the song which will be the target of the adjustment operation, and is similar to the Select Range window.

The selected range in the work sheet or staff sheet in the workspace is used as the initial selection, so you can preselect your target range instead, before invoking the adjustment command.

Controls

Track

Includes all tracks, or just the focus track, in the target range of the adjustment.

Some operations do not apply to some tracks.  For example, Velocitize cannot apply to the Lyrics track, since lyric events do not have a velocity.

Entire Song

Includes the whole length of the song in the target range of the adjustment.

Bar

Includes just the specified bar span in the target range of the adjustment.

Marker

Includes just the specified section in the target range of the adjustment.