XSelectInput(display, w, event_mask)
      Display *display;
      Window w;
      long event_mask;
| display | Specifies the connection to the X server. | 
| w | Specifies the window whose events you are interested in. | 
| event_mask | Specifies the event mask. | 
Setting the event-mask attribute of a window overrides any previous call for the same window but not for other clients. Multiple clients can select for the same events on the same window with the following restrictions:
The server reports the event to all interested clients.
XSelectInput() can generate a BadWindow error.
| BadWindow | A value for a Window argument does not name a defined Window. |