selection-mode-append-switch

See this command in the command table.

Home ribbon >> Select >> Append (toggle).
Using the command line, enter "selection-mode-append-switch".
On the Find Command screen, highlight selection-mode-append-switch and click Run.

Command Overview

Determines how data is selected or deselected in response to data selection in combination with the <CTRL> key.

There are two selection modes available:

Enabled: if data is selected by any method with the <CTRL> key held down, it will be added to the selection pool if it was not already selected. Data cannot be removed from the selection pool.
Disabled: data within the selection boundary will reverse its current state; selected data becomes unselected and vice versa.