What's the deal with "Warning: explicit element-wise assignment..."

[Steve Teale via Digitalmars-d]

On Tuesday, 15 April 2014 at 16:02:33 UTC, Steven Schveighoffer 
wrote:

> Sorry, I had this wrong. The [] on the left hand side is 
> actually part of the []= operator. But on the right hand side, 
> it simply is a [] operator, not tied to the =. I erroneously 
> thought the arr[] = ... syntax was special for arrays, but I 
> forgot that it's simply another operator.
>
> Steve, where do I find the []= operator in the documentation? 
> It does not seem to be under Expressions like the other 
> operators. Has it just not got there yet?
>
> Steve