-Each element looks like @code{(STRING . FUNCTION)}. STRING is
-content-transfer-encoding. FUNCTION is function to write decoded region
-to file.
-@end defvar
+First element of @var{spec} is service.@refill
+
+Rest of @var{args} is like an argument list of lambda, but (car (last
+@var{args})) must be specialized parameter. (car (car (last
+@var{args}))) is name of variable and (nth 1 (car (last @var{args}))) is
+name of backend (encoding).@refill
+
+Example:@refill
+
+@lisp
+(mel-define-method-function (mime-encode-string string (nil "base64"))
+ 'encode-base64-string)
+@end lisp
+@end defmac
+
+
+
+@node generic function for mel-backend, , mel-backend, Content-Transfer-Encoding
+@section How to add encoding/decoding service
+
+@defmac mel-define-service name &optional args doc-string
+
+Define @var{name} as a service for Content-Transfer-Encodings.@refill
+
+If @var{args} is specified, @var{name} is defined as a generic function
+for the service.@refill
+
+Example:@refill
+
+@lisp
+(mel-define-service encoded-text-encode-string (string encoding)
+ "Encode STRING as encoded-text using ENCODING.
+ENCODING must be string.")
+@end lisp
+@end defmac