use-empty-active-region

use-empty-active-region is a variable defined in `simple.el'.
Its value is

nil

Documentation:
Whether "region-aware" commands should act on empty regions.
If nil, region-aware commands treat empty regions as inactive.
If non-nil, region-aware commands treat the region as active as
long as the mark is active, even if the region is empty.

Region-aware commands are those that act on the region if it is
active and Transient Mark mode is enabled, and on the text near
point otherwise.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 23.1 of Emacs.