# Advance the `index` position to the next character
	#
	# Also set the `column`.
	# If the next character is a tab, compute the new column accordingly.
	private fun advance do
		var c = line_string.chars[index]
		if c == '\t' then
			index += 1
			column += column.columns_to_next_tab_stop
		else
			index += 1
			column += 1
		end
	end