* elmo-util.el (elmo-token-valid-p): New function.

* elmo-util.el (elmo-token-valid-p): New function.
(elmo-parse-token): Add optional argument `requirement'.
(elmo-parse-prefixed-element): Likewise.

* elmo-net.el (elmo-net-quote-chars): Renamed from
`elmo-net-quote-chars-regexp'.
(elmo-net-format-quoted): Add optional argument `extra-chars'.

* elmo-pop3.el (elmo-folder-initialize): Fix the token separators
by info document. Check token `uidl' is started an alphabet.

* elmo-nntp.el (elmo-folder-initialize): Fix the token separators
by info document. Check token `user' is started an alphabet.

* elmo-imap4.el (elmo-folder-initialize): Ditto.
(elmo-folder-list-subfolders): Quote user.