What's the rationale for considering "0x1.max" as invalid ?

[Basile B. via Digitalmars-d-learn]

On Tuesday, 5 April 2016 at 19:00:43 UTC, Basile B. wrote:
> 0x1.max // exponent expected in hex float
> 0x1 .max // OK
> 1.max // OK
>
> What's the ambiguity when it's an hex literal ?

https://issues.dlang.org/show_bug.cgi?id=15880