# Is `self` an hexadecimal digit ?
	#
	# ~~~
	# assert 'A'.is_hexdigit
	# assert not 'G'.is_hexdigit
	# assert 'a'.is_hexdigit
	# assert not 'g'.is_hexdigit
	# assert '5'.is_hexdigit
	# ~~~
	fun is_hexdigit: Bool do return (self >= '0' and self <= '9') or (self >= 'A' and self <= 'F') or
					(self >= 'a' and self <= 'f')