# Gets the numeric head of `self` if present
	# Returns "" otherwise
	#
	#     intrude import core::fixed_ints_text
	#     assert "0xFEFF".get_numhead  == "0x"
	#     assert "0b01001".get_numhead == "0b"
	#     assert "0o872".get_numhead   == "0o"
	#     assert "98".get_numhead      == ""
	private fun get_numhead: Text do
		if self.length < 2 then return ""
		var c = self[0]
		if c != '0' then return ""
		c = self[1]
		if c == 'x' or c == 'b' or c == 'o' or
		   c == 'X' or c == 'B' or c == 'O' then return substring(0, 2)
		return ""
	end