Hum, i really don't know how it is possible, because when I enter text here in the textbox and I hit enter (two times), like now
you can see I create two new lines, and that what I'm wanting to do.
To make your feature possible, for example here to preview, I must hit Tab to make Preview button have the focus, and here hitting enter send the preview.
Mozilla/5.0 (x11; U; Linux x86_64; fr-FR; rv:38.0) Gecko/20100101 Ubuntu/12.04 K-Meleon/76.0
Mail : alain [dot] aupeix [at] wanadoo [dot] fr
Ubuntu 12.04 - Gramps 3.4.9 - Harbour 3.2.0 - Hwgui 2.20-3 - K-Meleon 76.0 rc