D's Auto Decoding and You

[Vladimir Panteleev via Digitalmars-d-announce]

On Tuesday, 17 May 2016 at 17:26:59 UTC, Steven Schveighoffer 
wrote:
> However, it's perfectly legal for a front function not to be 
> tagged @property.

BTW, where is this coming from? Is it simply an emergent property 
of the existing implementations of isInputRange and ElementType, 
or is it actually by design?