Ask a user to select a safe coding system from candidates.
The candidates of coding systems which can safely encode a text
between FROM and TO are shown in a popup window. Among them, the most
proper one is suggested as the default.
The list of `buffer-file-coding-system' of the current buffer, the
default `buffer-file-coding-system', and the most preferred coding
system (if it corresponds to a MIME charset) is treated as the
default coding system list. Among them, the first one that safely
encodes the text is normally selected silently and returned without
any user interaction. See also the command `prefer-coding-system'.
However, the user is queried if the chosen coding system is
inconsistent with what would be selected by `find-auto-coding' from
coding cookies &c. if the contents of the region were read from a
file. (That could lead to data corruption in a file subsequently
re-visited and edited.)
Optional 3rd arg DEFAULT-CODING-SYSTEM specifies a coding system or a
list of coding systems to be prepended to the default coding system
list. However, if DEFAULT-CODING-SYSTEM is a list and the first
element is t, the cdr part is used as the default coding system list,
i.e. current `buffer-file-coding-system', default `buffer-file-coding-system',
and the most preferred coding system are not used.
Optional 4th arg ACCEPT-DEFAULT-P, if non-nil, is a function to
determine the acceptability of the silently selected coding system.
It is called with that coding system, and should return nil if it
should not be silently selected and thus user interaction is required.
Optional 5th arg FILE is the file name to use for this purpose.
That is different from `buffer-file-name' when handling `write-region'
(for example).
The variable `select-safe-coding-system-accept-default-p', if non-nil,
overrides ACCEPT-DEFAULT-P.
Kludgy feature: if FROM is a string, the string is the target text,
and TO is ignored.