Function enum_windows_proc 

pub unsafe extern "system" fn enum_windows_proc(
    hwnd: HWND,
    _l_param: LPARAM,
) -> BOOL

It receives top-level window handles and find windows with class SHELLDLL_DEF_VIEW_STR + child with WORKER_W_STR class

Read more: https://learn.microsoft.com/ru-ru/previous-versions/windows/desktop/legacy/ms633498(v=vs.85)