GameUI is the ancestor of non SimpleFrames. This is the overview Page. It only shows the direct children.
ORIGIN_FRAME_GAME_UI has on default 14 children. Multiboard, Leaderboard, TimerDialog, and QuestDialog are added when needed. With them it has 19.
After anyone clicked the QuestDialog 2 further ones are added.
Custom added Frames takes slots from [8] pushing others back after Chat/Log when created with prio(0)
[0] ORIGIN_FRAME_WORLD_FRAME [1] Probably Parent of World Object Hover info box & HP/Mana Bars [2] BottomUI Black Background "ConsoleUIBackdrop" [3] Parent of ORIGIN_FRAME_PORTRAIT [4] InventoryText, Related to the visuals of SimpleFrames, hiding it makes all SimpleFrames not visible but still clickable [5] Day Time Clock & Minimap are affected by this one, maybe ancestor/Parent [6] "CinematicPanel" [7] "ChatDialog"/"LogDialog" [8] "Multiboard" [9] "Leaderboard" [10] "TimerDialog" [11] No Idea [12] "QuestDialog" [13] "AllianceDialog" [14] No Idea [15] Parent Of "EscMenuBackdrop" [16] Chat Input [17] EscOptions [18] Mouse Cursor (Parent)