void pop(int depth);
/// pop one level off the cursor
void pop();
+ /// access to cursor 'tip'
+ CursorSlice & top() { return data_.back(); }
+ /// access to cursor 'tip'
+ CursorSlice const & top() const { return data_.back(); }
+
/// set the cell the cursor is in
void cell(int);
/// return the cell this cursor is in