Proposal:When should SystemBackdropElement be added to built-in controls, such as ToolTip, TeachingTip, and so on?

### Title

When should SystemBackdropElement be added to built-in controls, such as ToolTip, TeachingTip, and so on?

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什么时候为内置控件添加 SystemBackdropElement，例如 ToolTip，TeachingTip 等等？

### Summary

When should SystemBackdropElement be added to built-in controls, such as ToolTip, TeachingTip, and so on?

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什么时候为内置控件添加 SystemBackdropElement，例如 ToolTip，TeachingTip 等等？

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In the latest Windows App SDK 2.0-exp4 preview, a new control called SystemBackdropElement has been added to allow controls to use the SystemBackdrop feature. However, some built-in controls still use a solid color background in the latest exp4 and have not adopted the new SystemBackdrop feature. When will these built-in controls receive the SystemBackdrop?

Affected controls: ToolTip, TeachingTip, DatePicker, ComboBox, CommandBar.SecondaryCommands, TimePicker, CalendarDatePicker, NavigationView

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目前在最新的 Windows App SDK 2.0-exp4 预览版中新增了 SystemBackdropElement 这一控件用以为控件添加 SystemBackdrop 这一特性，然而部分内置控件到最新的 exp4 仍然使用纯色背景，没有添加最新的 SystemBackdrop。什么时候为这些内置控件添加 SystemBackdrop？

影响的控件：ToolTip，TeachingTip，DatePicker，ComboBox，CommandBar.SecondaryCommands，TimePicker，CalendarDatePicker，NavigationView

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Effect Graph(效果图)

### Rationale

None

### Scope

| Capability | Priority |
| :---------- | :------- |
| This proposal will allow developers to accomplish W | Must |
| This proposal will allow end users to accomplish X | Should |
| This proposal will allow developers to accomplish Y | Could |
| This proposal will allow end users to accomplish Z | Won't |

### Important Notes

None

### Open Questions

_No response_