display-buffer-reuse-frames is a variable defined in `window.el'.
Its value is
This variable is obsolete since 24.3;
use a `reusable-frames' alist entry in `display-buffer-alist'.
Non-nil means `display-buffer' should reuse frames.
If the buffer in question is already displayed in a frame, raise
You can customize this variable.
This variable was introduced, or its default value was changed, in
version 21.1 of Emacs.