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

[Basile B. via Digitalmars-d-learn]

On Tuesday, 5 April 2016 at 21:10:47 UTC, Basile B. wrote:
> On Tuesday, 5 April 2016 at 20:56:54 UTC, Alex Parrill wrote:
>> 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 ?
>>
>> It's potentially ambiguous with hexadecimal floating point 
>> numbers
>>
>> 0xdeadbeef.p5 // hex float or hex int + method?
>>
>> dlang.org/spec/lex.html#HexFloat
>
> Yes but it's pointless to allow the decimal separator to be 
> followed by the exponent:
>
> void main()
> {
>     import std.stdio;
>     writeln( typeof(0x1p5).stringof ); // double
>     writeln( typeof(0x1.p5).stringof ); // double
> }

I mean that the rule could be: the decimal separator must be 
followed by a second group of digits. The second group of digits 
must be followed by an exponent. The first group of digits can be 
followed by an exponent.

0x1.0p5 // valid
0xp5 // valid
0x1.p5 // invalid (p is not a hex digit)
0x1.ap5 // valid