Changing a user agent string [CODE INCLUDED]

[Boruch Baum <boruch_baum@xxxxxxx>]

I wanted to easily see how pages might appear differently using
different user-agent strings, so I wrote the following. If there is
interest to add it to the project, I would change the alist to a
defcustom.

If anyone on the list has any helpful experience to share regarding
useful user-agent strings, I would welcome hearing about it.

-- 
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; User-agent strings
(setq w3m-user-agent-alist (list
  (cons "Emacs-w3m (user default)" w3m-user-agent)
  (cons "Emacs-w3m (package default)" (concat "Emacs-w3m/" emacs-w3m-version " " w3m-version))
  '("Don't send user agent" . "")
  '("Android Webkit" . "Mozilla/5.0 (Linux; U; Android 4.0.3; ko-kr; LG-L160L Build/IML74K) AppleWebkit/534.30 (KHTML, like Gecko) Version/4.0 Mobile Safari/534.30")
  '("IE Mobile" . "Mozilla/5.0 (compatible; MSIE 9.0; Windows Phone OS 7.5; Trident/5.0; IEMobile/9.0)")
  '("Opera Mini 9.80" . "Opera/9.80 (J2ME/MIDP; Opera Mini/9.80 (S60; SymbOS; Opera Mobi/23.348; U; en) Presto/2.5.25 Version/10.54")
  '("Opera Mobile 12" . "Opera/12.02 (Android 4.1; Linux; Opera Mobi/ADR-1111101157; U; en-US) Presto/2.9.201 Version/12.02")
  '("Chrome 51" . "Mozilla/5.0 (Linux; Android 5.1.1; VS810PP Build/LMY47V) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.81 Mobile Safari/537.36")))

(defun w3m-user-agent-change (&optional ua-string)
"Change the user-agent string.
The function prompts the user to select from entries in
`w3m-user-agent-alist', or the user may manually enter a custom
user-agent string. This function also updates `w3m-add-user-agent'."
  (interactive "P")
  (when (not ua-string)
    (setq ua-string
      (or (cdr (assoc (setq ua-string
                        (completing-read "Select a user-agent: " w3m-user-agent-alist))
                w3m-user-agent-alist))
          ua-string)))
  (cond
   ((or (not ua-string) (string-equal ua-string ""))
     (setq w3m-add-user-agent nil))
   (t
     (setq w3m-add-user-agent t)
     (setq w3m-user-agent ua-string))))