Demo: Made the "menu inside a regular window" be in a different menuset. Added a comment (#409)

imgui_demo.cpp

@@ -1098,14 +1098,20 @@ void ImGui::ShowTestWindow(bool* opened)
                 ImGui::EndPopup();
             }
 
+            ImGui::Spacing();
             ImGui::TextWrapped("Below we are testing adding menu items to a regular window. It's rather unusual but should work!");
             ImGui::Separator();
+            // NB: As a quirk in this very specific example, we want to differentiate the parent of this menu from the parent of the various popup menus above. 
+            // To do so we are encloding the items in a PushID()/PopID() block to make them two different menusets. If we don't, opening any popup above and hovering our menu here
+            // would open it. This is because once a menu is active, we allow to switch to a sibling menu by just hovering on it, which is the desired behavior for regular menus.
+            ImGui::PushID("foo");
             ImGui::MenuItem("Menu item", "CTRL+M");
-            if (ImGui::BeginMenu("Menu"))
+            if (ImGui::BeginMenu("Menu inside a regular window"))
             {
                 ShowExampleMenuFile();
                 ImGui::EndMenu();
             }
+            ImGui::PopID();
             ImGui::Separator();
 
             ImGui::TreePop();