WM_SETTEXT

  This message is sent to a window when the application wants to set the
text of that window. For edit controls this text is the contants of the
edit buffer. For button controls, this text is the button name. For all
other windows, this text is the window's caption.

Parameters
  wParam is not used.
  lParam is a far pointer to a buffer that contains a null-terminated string
   which will be the text for that window.