void CmdDeleteBackword()
{
int pos = WordBackward(cursor);
if (pos == -1)
return;
string k = text.ToString(pos, cursor - pos);
if (last_handler == CmdDeleteBackword)
kill_buffer = k + kill_buffer;
else
kill_buffer = k;
text.Remove(pos, cursor - pos);
ComputeRendered();
RenderAfter(pos);
}