Assembly / Single Object Selection switch
Command : Prb_AssemblySelection

This switch is also accessible from the status bar of AutoCAD and BricsCAD.
The status bar in AutoCAD

The status bar in BricsCAD
This command functions like a ‘switch’. Every time you click on it the assembly selection is turned on or off.
All components of one assembly are grouped together. If you turn off assembly selection, then you can for example move a welded plate without moving all of its assembly members at the same time. The groups will always stay intact, i.e. when you turn assembly selection back on all components of that assembly will ‘stick together again’.
To make things clear: assembly selection only changes something about the way in which elements are selected while drawing, not which element is attached to what other elements. So the assembly data remains intact after the assembly selection has been turned on or off.