`mime-preview-quitting-method-alist'.
'gnus-original-article-mode
(function mime-text-decode-buffer))
-(set-alist 'mime-view-quitting-method-alist
- 'gnus-original-article-mode
- (function mime-view-quitting-method-for-gnus))
+(set-alist 'mime-preview-quitting-method-alist
+ 'gnus-original-article-mode #'mime-view-quitting-method-for-gnus)
(set-alist 'mime-view-show-summary-method
'gnus-original-article-mode