A question about macro bindings in cl-lib

[Xue Fuqiao <xfq.free@gmail.com>]

In (info "(cl) Macro Bindings"):

  (cl-defmacro my-dolist ((x list) &rest body)
    (let ((var (cl-gensym)))
      (list 'cl-loop 'for var 'on list 'do
            (cl-list* 'cl-symbol-macrolet
                      (list (list x (list 'car var)))
                      body))))
  (setq mylist '(1 2 3 4))
  (my-dolist (x mylist) (cl-incf x))
  mylist
       => (2 3 4 5)

  The `my-dolist' call shown here expands to

  (cl-loop for G1234 on mylist do
        (cl-symbol-macrolet ((x (car G1234)))
          (cl-incf x)))

I understand what this macro does, but what does "G1234" mean here?  (I
have searched the archives, but "No document matching your query".)

--
Best regards, Xue Fuqiao.
http://www.gnu.org/software/emacs/