Here is the relevant part of my .xbindkeysrc file. The first commented line gives you idea of what I am trying to achieve.
# System-wide equivalence of Shift-Del, Ctrl-Ins, Shift-Ins and Ctrl-X, Ctrl-C, Ctrl-V, respectively
# "xvkbd -xsendevent -text '\Cx'"
"xdotool key 'Control_L+x'"
Shift + Delete + Release
# "xvkbd -xsendevent -text '\Cc'"
"xdotool key 'Control_L+c'"
Control + Insert + Release
# "xvkbd -xsendevent -text '\Cv'"
"xdotool key 'Control_L+v'"
Shift + Insert + Release
At the beginning, I was totally happy with solution based on xvkbd utility (commented lines), until I realised it did not work in Gnome applications.
So I had to switch to xdotools in stead. For some reasons, it is only the second block (corresponding to the copying operation) that is working. I need your advice on what to change in the other two blocks.