returns 'ascii' if the encoding is unknown to the library.

		Certain heuristics are performed to recover data from bytes that are
		ill-formed in the chosen encoding, or that otherwise look misencoded
		(mostly around bad UTF-16BE encoded bytes, or bytes that look like UTF-16BE
		but marked otherwise).  If the bytes are ill-formed and the heuristics fail,
		the error is handled according to the errors parameter to this function, which is
		passed to the underlying decode() function; by default it throws a
		UnicodeDecodeError exception.

		Note: The mentioned heuristics mean that roundtripping a font to XML and back
		to binary might recover some misencoded data whereas just loading the font
		and saving it back will not change them.
		c