I do think that, in specific technical contexts, a useful distinction (though still fuzzy on the margins) can be made between programming languages and markup languages.
that is my real point
I also did not say HTML is not a programming language.
Doesn't the "to be rendered" part make it instructions? Its like there are two labels for a bottle of poison: "poison" and "poison: do not drink". But the label that says "poison" is of a shape, color, and design that is commonly understood to be a label that tells the reader not to imbibe the contents of the bottle to which it is attached.
It's not turing complete. There are limits to the types of computation that can be performed with it.
It's not silly -- it's a meaningful distinction.
As an example: if you use a Game Maker application to construct a video game where your inputs are the graphics, the level design, and some basic scripting to connect them up, is the resulting output "not a program" because the input scheme that you used in order to define its behavior was not Turing Complete? You could make an argument that, in the context of Quines, this isn't relevant because the Program is not outputting its own source code but only the top-most layer of its definition, but then again that's true at some level for any Quine not written in machine code (and even then it'd probably be missing much of the OS / display drivers / etc.).
Edit: removed an example about "programmable TV remotes" because it wasn't a very good example, and added a note about Quines.
Limitations of those instructions is the key aspect. You couldn't use any English or natural language expression for example. It might seem obvious but complexity of those instructions is what makes the language abstract. Having complicated instructions isn't always desireable though e.g. the CISC vs RISC debate.
An HTML file cannot be a Quine because an HTML file is not a program because HTML is not Turing Complete.
Adding two numbers in HTML might be expressable but clearly it's much easier in Javascript.
Cellular automation is Turing-complete, but is not a program.
Turing-complete is a fun thing to talk about in college theory classes, but has limited practical use outside of academia.
https://github.com/ainfosec/crema
Also, you can generate RSA key pairs using HTML: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/ke...
IMHO, the better mental model is that HTML is a declarative programming language that is very abstract.
My point is let's stop being so pedantic in the soft spaces. This isn't a discussion about "should I use HTML to write my kernel?"
For example, a Lisp based on JSON:
https://github.com/kanaka/miniMAL
A program:
["+", 2, 3]
I suppose this is still not a proof that JSON is (or can be) a programming language, since it covers only the notation.