Fixtype of hexadecimal fractional constants [C:6.4.4.2] [C:A.1.5].
This is a product type introduced by fty::defprod.
This corresponds to hexadecimal-fractional-constant in the grammar in [C]. It consists of the digits before and after the point. Thus, it covers the three possibilities of (i) the point in the middle (with a left and right digit sequence), (ii) the point at the start (with just a right digit sequence), and (iii) the point at the end (with just a left digit sequence); it also covers a fourth possibility, disalowed in the grammar in [C], namely when there are no digits before or after the point. This fourth possibilty makes the definition of this fixtype simpler, and can be ruled out by predicates over this abstract syntax.