Andreas Brauchli authored Aug 20, 2016 and Jens Georg committed Feb 23, 2019

Holding CTRL or SHIFT while selecting a marker now has the same effect
as in the library window and the marker selection will be toggled.

If a group marker that is shown as selected (because it contains a selected
marker) is pressed, the selection will be cleared when clicked while
holding modifiers CTRL or SHIFT.