Variable: Info-current-subfile
Info-current-subfile is a buffer-local variable defined in info.el.gz.
Documentation
Info subfile that is actually in the *info* buffer now.
It is nil if current Info file is not split into subfiles.
Source Code
;; Defined in /usr/src/emacs/lisp/info.el.gz
(defvar-local Info-current-subfile nil
"Info subfile that is actually in the *info* buffer now.
It is nil if current Info file is not split into subfiles.")