Function scoped 

pub fn scoped(keycaps: Keycaps) -> ScopedKeycaps

Read keycaps as the active layout on this thread only, until the returned guard drops; the previous scope comes back then, even when the holder panics. For code that renders labels under a given layout (a test asking for German keycaps) without changing what every other thread reads: set_active is process-wide, so a test using it would leak its layout into every test running beside it.