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Reproduction steps:
1. Create a new project
2. Create HelpBox Standard Element (GameObject > UI Toolkit > Standard Elements > Unity > UI > Builder > Help Box)
3. Create UI Document
4. Observe the Console
Actual result: "IMGUIContainer cannot be used in a runtime panel" errors are thrown
Expected result: No errors or warnings are thrown when adding Elements from UI Library window
Reproducible with: 6000.6.0a7, 6000.6.0b2, 6000.7.0a1
Couldn’t reproduce with: 6000.0.78f1, 6000.3.19f1, 6000.5.2f1, 6000.6.0a6 (No Standard Elements option)
Reproduced on: Ubuntu 24.04, macOS Tahoe 26.5 (M4)
Note: Full errors:
IMGUIContainer cannot be used in a runtime panel. UnityEngine.UIElements.Panel:Repaint () Unity.UIToolkit.Editor.PanelElement:FrameUpdate () Unity.UIToolkit.Editor.VisualElementEditingStage:RequestRefresh () Unity.UIToolkit.Editor.MenuUtility:ExecuteAdd (Unity.UIToolkit.Editor.VisualElementEditingStage,System.Type,UnityEngine.UIElements.VisualElementAsset) Unity.UIToolkit.Editor.MenuUtility:EnterStageAndAdd (Unity.UIToolkit.Editor.VisualTreeAssetEditingContext,System.Type,UnityEngine.UIElements.VisualElementAsset) Unity.UIToolkit.Editor.MenuUtility:AddInAppropriatePanelRendererComponent (UnityEngine.GameObject,System.Type,bool) Unity.UIToolkit.Editor.MenuUtility:AddElement (System.Type,bool,bool) Unity.UIToolkit.Editor.MenuUtility:AddElementAsSibling (System.Type) Unity.UIToolkit.Editor.UIElementsProvider:AddElementToVisualTreeAsset (UnityEditor.Search.SearchItem) UnityEditor.Search.HierarchySearchItemHandler:Unity.Hierarchy.IHierarchyEditorNodeTypeHandler.OnDoubleClick (Unity.Hierarchy.HierarchyView,Unity.Hierarchy.HierarchyNode modreq(System.Runtime.InteropServices.InAttribute)&) Unity.Hierarchy.HierarchyView:OnClickEvent (UnityEngine.UIElements.ClickEvent) UnityEditor.GUIView:ProcessEvent (UnityEngine.EntityId,intptr,bool&)
IMGUIContainer cannot be used in a runtime panel. UnityEngine.UIElements.UIElementsRuntimeUtilityNative:RepaintPanels (bool)
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