I have two questions about xkb grp's. First, when I look at the defined grp's, I see a description for some that says "while pressed". What exactly does this mean? Aren't all of these shortcuts based on key pressed? See attached image for what I mean.
Second, I'd like to add a grp. I am using the XFCE build, and when I try to configure the keyboard shortcut used for switching my keyboard layout, I'd like to use a key combo that is not listed in the pre-defined grp's, but the only options available (through the GUI) are the pre-defined grp's. For example, I'd like to have a group like "ctrl+shift+L".