+(defcustom mm-w3m-safe-url-regexp "\\`cid:"
+ "Regexp that matches safe url names. Some HTML mails might have a
+trick of spammers using <img> tags. It is likely to be intended to
+verify whether you have read the mail. You can prevent your personal
+informations from leaking by setting this to the regexp which matches
+the safe url names. The value of the variable `w3m-safe-url-regexp'
+will be bound with this value. You may set this value to nil if you
+consider all the urls to be safe."
+ :type '(choice (regexp :tag "Regexp")
+ (const :tag "All URLs are safe" nil)
+ :group 'mime-display))
+