# Is `self` a valid hexadecimal digit (in ASCII)
	#
	# ~~~nit
	# intrude import core::bytes
	# assert not u'/'.is_valid_hexdigit
	# assert u'0'.is_valid_hexdigit
	# assert u'9'.is_valid_hexdigit
	# assert not u':'.is_valid_hexdigit
	# assert not u'@'.is_valid_hexdigit
	# assert u'A'.is_valid_hexdigit
	# assert u'F'.is_valid_hexdigit
	# assert not u'G'.is_valid_hexdigit
	# assert not u'`'.is_valid_hexdigit
	# assert u'a'.is_valid_hexdigit
	# assert u'f'.is_valid_hexdigit
	# assert not u'g'.is_valid_hexdigit
	# ~~~
	private fun is_valid_hexdigit: Bool do
		return (self >= 0x30 and self <= 0x39) or
		       (self >= 0x41 and self <= 0x46) or
		       (self >= 0x61 and self <= 0x66)
	end