|ext:open-using-scheme scheme pathname filename &key direction element-type if-exists if-does-not-exist external-format||[Generic Function]|
Open the pathname returning the open file, as for open. Called by open after translating the original filename to a pathname. Two values are returned: a stream or nil, and a success flag. When the direction includes input, the success flag is true when the file is found. If the direction is output then the success flag is true when a path was found at which the file could be opened.