property functions

[Nick]

The [Property 
Functions](https://dlang.org/spec/function.html#property-functions) documentation reads:

> WARNING: The definition and usefulness of property functions is 
> being reviewed, and the implementation is currently incomplete. 
> Using property functions is not recommended until the 
> definition is more certain and implementation more mature.

Is this warning still valid? The standard library appears to 
extensively use property functions.