Variable: TeX-master

TeX-master is a customizable and buffer-local variable defined in tex.el.

Documentation

The master file associated with the current buffer.

If the file being edited is actually included from another file, you can tell AUCTeX the name of the master file by setting this variable. If there are multiple levels of nesting, specify the top level file.

If this variable is nil, AUCTeX will query you for the name.

If the variable is t, AUCTeX will assume the file is a master file itself.

If the variable is shared, AUCTeX will query for the name, but not change the file.

If the variable is dwim, AUCTeX will try to avoid querying by attempting to do what I mean; and then change the file.

It is suggested that you use the File Variables (see the info node
(emacs)File Variables) to set this variable permanently for each file.

Source Code

;; Defined in ~/.emacs.d/elpa/auctex-14.1.2/tex.el
;;; Master File

(defcustom TeX-master t
  "The master file associated with the current buffer.
If the file being edited is actually included from another file, you
can tell AUCTeX the name of the master file by setting this variable.
If there are multiple levels of nesting, specify the top level file.

If this variable is nil, AUCTeX will query you for the name.

If the variable is t, AUCTeX will assume the file is a master file
itself.

If the variable is `shared', AUCTeX will query for the name, but not
change the file.

If the variable is `dwim', AUCTeX will try to avoid querying by
attempting to `do what I mean'; and then change the file.

It is suggested that you use the File Variables (see the info node
`File Variables') to set this variable permanently for each file."
  :group 'TeX-command
  :group 'TeX-parse
  :type '(choice (const :tag "Query" nil)
                 (const :tag "This file" t)
                 (const :tag "Shared" shared)
                 (const :tag "Dwim" dwim)
                 (string :format "%v"))
  :safe (lambda (x)
          (or (stringp x)
              (member x (quote (t nil shared dwim)))))
  :local t)