When the mouse is over a variable or macro definition a tooltip is shown with useful information. It is sometimes useful to copy this information (documentation, checkin a macro expansion...), it is however not possible to right click and copy or ctrl+v
Ctrl+C works for me, however it's not discoverable.
I checked again in version 5.3.1 and it in deed works with Ctrl+C, it didn't work before. I think this can be closed Thanks