Returns the results or null on failure. Returns true on success, false on failure. This is the best method I can think of to preserve the original file's integrity should a conflict or error occur. This method should be relatively safe from process conflicts. If the old file does not exist or if the new file already exists, this method will abort and return false.
Returns null if unable to read the contents of the directory.
Given a user ID, will return true if that user id owns the specified file. If UID is not specified, the method assumes itself. If the UID is specified, will return true of that UID is the owner of the specified file, false otherwise. This method will return the user ID of the PHP process itself. The results of this method are cached by the class for more efficient results.