{"ast_node_type":"other","tokens":[{"end":86,"kind":"keyword","start":0,"text":"//"}]}
        // Crucially, we go via `AllocBytes::as_mut_ptr`, not `AllocBytes::deref_mut`.
        assert!(range.end().bytes_usize() <= self.bytes.len()); // need to do our own bounds-check
        let begin_ptr = self.bytes.as_mut_ptr().wrapping_add(range.start.bytes_usize());