The docs currently say:

"Note that there are some alternative ways to initialize GTK+: if you are calling gtk_parse_args(), gtk_init_check(), gtk_init_with_args() or g_option_context_parse() with the option group returned by gtk_get_option_group(), you don't have to call gtk_init()."

The part "you don't have to..." is only partially true.  If I want to parse arguments, then fork, then open display I have to use either gtk_parse_args() or gtk_get_option_group(FALSE), then fork, then call gtk_init().

The docs for gtk_parse_args() also say: "You shouldn't call this function explicitely if you are using gtk_init(), or gtk_init_check()."  The "shouldn't" part is wrong.  It should be "You don't need".