[编程交流] 这2个代码，分别有多大的区别和优势？

;; Start Undo  -  Lee Mac
;; Opens an Undo Group.

(defun LM:startundo ( doc )
    (LM:endundo doc)
    (vla-startundomark doc)
)

;; End Undo  -  Lee Mac
;; Closes an Undo Group.

(defun LM:endundo ( doc )
    (while (= 8 (logand 8 (getvar 'undoctl)))
        (vla-endundomark doc)
    )
)

;; Active Document  -  Lee Mac
;; Returns the VLA Active Document Object

(defun LM:acdoc nil
    (eval (list 'defun 'LM:acdoc 'nil (vla-get-activedocument (vlax-get-acad-object))))
    (LM:acdoc)
)

(setq doc (vla-get-activedocument (vlax-get-acad-object)))
(vla-startundomark doc)
(vla-endundomark doc)