Happens immediately after the window is created (ie, while you're calling GuiCreateWindow -- GuiCreateWindow actually calls your CREATE event handler), but not yet shown. Modifications can be made to the window, or resources needed by this window may be allocated.
Return
An empty string to finish creating the window. If you instead return no value, then the window will not be created, and GuiCreateWindow will have an error.
Notes
No controls have yet been added to the window. But you may add controls to the window using GuiAddCtl.
See also: DESTROY, NCCREATE.