datastore/query.go
func (q *Query) Offset(offset int) *Query {
	q = q.clone()
	if offset < 0 {
		q.err = errors.New("datastore: negative query offset")
		return q
	}
	if offset > math.MaxInt32 {
		q.err = errors.New("datastore: query offset overflow")
		return q
	}
	q.offset = int32(offset)
	return q
}
func (q *Query) Offset(offset int) *Query {
	q = q.clone()
	if offset < 0 {
		q.err = errors.New("datastore: negative query offset")
		return q
	}
	if offset > math.MaxInt32 {
		q.err = errors.New("datastore: query offset overflow")
		return q
	}
	q.offset = int32(offset)
	return q
}
// Offset returns a derivative query that has an offset of how many keys to
// skip over before returning results. A negative value is invalid.