--- Closes file, or the default output file.
function close([file])
--- Flushes the default output file.
function flush()
---
-- Opens file in text mode, sets as default input file, or returns current
-- default input file.
function input([file])
--- Open file in read mode, returns iterator function to return lines, nil ends.
function lines([filename])
--- Opens file in specified mode "[rawb+]", returns handle or nil.
function open(filename [, mode])
---
-- Opens file in text mode, sets as default output file, or returns current
-- default output file.
function output([file])
--- Reads file according to given formats, returns read values or nil.
function read(format1, ...)
-- * `stderr`: File descriptor for STDERR.
-- * `stdin`: File descriptor for STDIN.
-- * `stdout`: File descriptor for STDOUT.
--- Returns a handle for a temporary file, opened in update mode.
function tmpfile()
---
-- Returns "file" if obj is an open file handle, "close file" if closed, or nil
-- if not a file handle.
function type(obj)
--- Writes strings or numbers to file.
function write(value1, ...)

---
-- Opens a list of files.
-- @param utf8_filenames A '\n' separated list of filenames to open. If none
--   specified, the user is prompted to open files from a dialog. These paths
--   must be encoded in UTF-8.
-- @usage io.open_file(utf8_encoded_filename)
function open_file(utf8_filenames)

---
-- Saves all dirty buffers to their respective files.
-- @usage io.save_all()
function save_all()

---
-- Closes all open buffers.
-- If any buffer is dirty, the user is prompted to continue. No buffers are
-- saved automatically. They must be saved manually.
-- @usage io.close_all()
-- @return true if user did not cancel.
function close_all()