MultiSelect: Comments + tweaked location for widgets to test ImGuiItemFlags_IsMultiSelect to avoid misleading into thinking doing it before ItemAdd() is necessary.

imgui_internal.h

@@ -1757,7 +1757,7 @@ struct IMGUI_API ImGuiMultiSelectTempData
     ImS8                    LoopRequestSetAll;  // -1: no operation, 0: clear all, 1: select all.
     bool                    IsEndIO;            // Set when switching IO from BeginMultiSelect() to EndMultiSelect() state.
     bool                    IsFocused;          // Set if currently focusing the selection scope (any item of the selection). May be used if you have custom shortcut associated to selection.
-    bool                    IsSetRange;         // Set by BeginMultiSelect() when using Shift+Navigation. Because scrolling may be affected we can't afford a frame of lag with Shift+Navigation.
+    bool                    IsKeyboardSetRange; // Set by BeginMultiSelect() when using Shift+Navigation. Because scrolling may be affected we can't afford a frame of lag with Shift+Navigation.
     bool                    NavIdPassedBy;
     bool                    RangeSrcPassedBy;   // Set by the item that matches RangeSrcItem.
     bool                    RangeDstPassedBy;   // Set by the item that matches NavJustMovedToId when IsSetRange is set.
@@ -1765,7 +1765,7 @@ struct IMGUI_API ImGuiMultiSelectTempData
 
     ImGuiMultiSelectTempData()  { Clear(); }
     void Clear()            { size_t io_sz = sizeof(IO); ClearIO(); memset((void*)(&IO + 1), 0, sizeof(*this) - io_sz); } // Zero-clear except IO as we preserve IO.Requests[] buffer allocation.
-    void ClearIO()          { IO.Requests.resize(0); IO.RangeSrcItem = IO.NavIdItem = (ImGuiSelectionUserData)-1; IO.NavIdSelected = IO.RangeSrcReset = false; }
+    void ClearIO()          { IO.Requests.resize(0); IO.RangeSrcItem = IO.NavIdItem = ImGuiSelectionUserData_Invalid; IO.NavIdSelected = IO.RangeSrcReset = false; }
 };
 
 // Persistent storage for multi-select (as long as selection is alive)