/// Opaque type for World pointers.
/// Opaque type for QueryBuilder pointers.
/// Opaque type for QueryState pointers.
/// Opaque type for Query pointers.
/// Opaque type for QueryIter pointers.
/// Opaque type for FilteredEntityMut pointers.
/// Opaque type for ParamBuilder pointers.
/// Opaque type for SystemState pointers.
/// Opaque type for DynSystemParams pointers.
/// Opaque type for System pointers.