Variable: tags-add-tables
tags-add-tables is a customizable variable defined in etags.el.gz.
Value
ask-user
Documentation
Control whether to add a new tags table to the current list.
t means do; nil means don't (always start a new list). Any other value means ask the user whether to add a new tags table to the current list (as opposed to starting a new list).
Source Code
;; Defined in /usr/src/emacs/lisp/progmodes/etags.el.gz
;; !!! tags-compression-info-list should probably be replaced by access
;; to directory list and matching jka-compr-compression-info-list. Currently,
;; this implementation forces each modification of
;; jka-compr-compression-info-list to be reflected in this var.
;; An alternative could be to say that introducing a special
;; element in this list (e.g. t) means : try at this point
;; using directory listing and regexp matching using
;; jka-compr-compression-info-list.
;;;###autoload
(defcustom tags-add-tables 'ask-user
"Control whether to add a new tags table to the current list.
t means do; nil means don't (always start a new list).
Any other value means ask the user whether to add a new tags table
to the current list (as opposed to starting a new list)."
:type '(choice (const :tag "Do" t)
(const :tag "Don't" nil)
(other :tag "Ask" ask-user)))