List of information about understood file formats.
Elements are of the form
(NAME DOC-STR REGEXP FROM-FN TO-FN MODIFY MODE-FN PRESERVE).
NAME is a symbol, which is stored in `buffer-file-format'.
DOC-STR should be a single line providing more information about the
format. It is currently unused, but in the future will be shown to
the user if they ask for more information.
REGEXP is a regular expression to match against the beginning of the file;
it should match only files in that format. REGEXP may be nil, in
which case the format will never be applied automatically to a file.
Use this for formats that you only ever want to apply manually.
FROM-FN is called to decode files in that format; it takes two args, BEGIN
and END, and can make any modifications it likes, returning the new
end. It must make sure that the beginning of the file no longer
matches REGEXP, or else it will get called again.
Alternatively, FROM-FN can be a string, which specifies a shell command
(including options) to be used as a filter to perform the conversion.
TO-FN is called to encode a region into that format; it takes three
arguments: BEGIN, END, and BUFFER. BUFFER is the original buffer that
the data being written came from, which the function could use, for
example, to find the values of local variables. TO-FN should either
return a list of annotations like `write-region-annotate-functions',
or modify the region and return the new end.
Alternatively, TO-FN can be a string, which specifies a shell command
(including options) to be used as a filter to perform the conversion.
MODIFY, if non-nil, means the TO-FN wants to modify the region. If nil,
TO-FN will not make any changes but will instead return a list of
annotations.
MODE-FN, if specified, is called when visiting a file with that format.
It is called with a single positive argument, on the assumption
that this would turn on some minor mode.
PRESERVE, if non-nil, means that `format-write-file' should not remove
this format from `buffer-file-format'.