code: func (r Range) Apply(q *datastore.Query) *datastore.Query {
  	if r.Start != nil {
  		q = q.Gt("__key__", r.Start)
  	}
  	if r.End != nil {
  		q = q.Lte("__key__", r.End)
  	}
  	return q
  }
docs: // Apply adds >Start and <=End filters to the query and returns the resulting
  // query.