Filed as a result of the FragmentShader survey.

Users were unclear that clip rects can be used to limit the scope of BackdropFilter with ImageFilter.shader. This is documented in the BackdropFilter classes documentation. We should add a link to it in:

• ImageFilter.shader documentation
• The FragmentShader documentation ( https://docs.flutter.dev/ui/design/graphics/fragment-shaders ) - This has been updated recently to show an example with a clip rect, but it doesn't explain why.