>Neither the name “Markdown” nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission.
Gruber is not being irrational. He is operating under a different paradigm, which he explained last time Marco Arment was on his podcast. He is approaching this from the view that the optimal markdown implementation for a code site like GitHub is different to the optimal markdown for a commenting site like Reddit. Standardisation just locks in a suboptimal implementation for everyone. Whether you agree or disagree, it's at least a rational viewpoint.
The creator of the project let you do anything with it other than use the name markdown for a derivative product. They went ahead and did that. A completely unreasonable move that is just spiteful.
Documenting your own Markdown flavour will be easier if you can say "It's Standard Markdown, plus/except these features...", instead of "It's part of the soupy world of 'Markdown', but here are the features that some/all other implementations don't have...".
> He did copyright everything. Explicitly.
I didn't realise that. In that case he can force them to change it if he doesn't like it, right? I don't get why people are talking about honour/decency.
This has nothing to do with my view point, it's simply a fact of law: you can't copyright a name. No matter what text you put somewhere says, it doesn't magically apply.
Another way to look at it is this is just another implementation of markdown -- one that some of the bigger names in the markdown-business are going to support moving forward.
Gruber seems to be a bit of a dick about it. Maybe he got surprised and it hit him harder than expected today. No surprise though, he's now about to be usurped. He sat on his hands for years. In the release today (and forever) they give him large amounts of due credit. The Talk Show crowd (I'm a listener) will grumble, and fanboys on Twitter will support him and jeer Atwood personally, but oh welp. There's one party actually advancing technology, the other resting on laurels.
He kind of mentioned being a benevolent dictator on the [podcast 88 discussion](https://overcast.fm/podcasts/episode/344902019595#t=4527), but what important decisions has he actually made lately? It seems to me he just points back to his implemention perl script. Genuine question. He hasn't made a spec because (loosely) "why have a spec; just do whatever you want, take a look over here".
So it's a variant of his perl script. Great, that sounds exactly as he mused everyone should do. I can see how it rubs him the wrong way with "Standard Markdown".
Also: by doing this, the group will be forcing his hand. They've released it magnanimously, invited him to be a part of the process for years. He didn't respond in kind, labeling it "Atwood's crusade".
He may not like the name "Standard" enough to do something about it. He can choose to pursue legal options. I doubt he wants to spend any money on that. You've got to assume GH, SO, and Reddit went over the Markdown license on DaringFireball.
He can choose to be grumpy about it, but this is happening. Those 3 entities have massive persuasive force with their user bases; enough to become standard.
Ambiguity is not a feature it is a bug. It is not optimal.
This "Standard" makes things even worse. There are plenty of sites already on the internet that say they accept "Markdown", and that meant something: that it implements Gruber's formatting, and perhaps some extensions (and sites with extensions are normally clear about the fact that they're extensions, e.g. "Github-flavoured Markdown"). Now people will see a site that accepts "Markdown", expect it to support a feature from "Standard Markdown", and get angry when it doesn't.
Markdown is not for that and the exact reason to use it is that every site could customize it for their usage. Contrary to your assertions (which I see is backed by no argument) abiguity in markdown is a feature. Ambiguity in HTML was a bug.