What is this "dd" doc format?

[Meta]

On Tuesday, 19 December 2017 at 20:20:16 UTC, John Gabriele wrote:
> I just went looking for the source for the dlang.org overview 
> page, and found 
> [this](https://github.com/dlang/dlang.org/blob/master/overview.dd).
>
> I've seen and used a lot of markup formats, but have never run 
> across this. What format is it? Also curious: for what reasons 
> was it chosen over a more customary markup?
>
> Thanks.

https://dlang.org/spec/ddoc.html

When D was first created there was no clear documentation 
solution (as far as I know. I was not a programmer back then), so 
Walter invented DDOC. Actually it's a general text macro system 
and is not markup language or a documentation generation system, 
which may be why it seems so strange if you're used to stuff like 
javadoc/doxygen/etc.