Spacing between Primary and Secondary Groups

Use

Spacing around secondary groups

The spacing around grouping controls of the type "primary group" and "secondary group", i.e., groups without a border and without a header area, should be 10 pixels.

Example of spacing around secondary groups

The caesuras clearly stress three areas, realized as three groups.

Example of wrong spacing around secondary groups

A smaller offset blurs the contrast between secondary group control and the tray's background.