This function creates new window on server side (by sending open_window command to the server) and YwWindow helper structure on client side. YwWindow supports all primitive window operations, like drawing, scrolling, etc. Window is connected to server through conn. taglist contains parameters of created window. This function fetches for own purpouses "width", "virtual_width", "height" and "virtual_height". However entire packet is passed to server (and then to WM) untouched.