Black rubber gasket from front panel assembly

During the replacement of an iPhone 5 front panel assembly a small rubber gasket fell out from the earpiece speaker area. This is a flexible piece of rubber and not the small plastic spacer from the earpiece speaker area. Does anyone know what this small rubber gasket is and where it goes? Thanks!

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This goes over the pink / purple sensor part located on the front camera ribbon cable assembly (I think this sensor is to check how much light is going in for auto-brightness)

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Thank you, Ben!

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