> No, not with strictly sticking to the standard and not use any trickery. HTML was not designed to do any kind of calculation. That's why javascript came later.

I thought you would go here, and I understand where you are coming from: Declarative language != file format and declarative is not a paradigm like functional, procedural, object-oriented.

Every useful declarative language allows for some level of computation. Take a template language - YAML + some template tags. Aside allowing variable substitution, every time, the language grows a way to make those substitutions more useful, so you get things like:

{{ variable_containing_a_date + interval(days=1) }}

Back to functional, oo, procedural: some declarative languages import a paradigm.

Back to the script tag:

Even though it was added after the original spec, <script> is part of the standard for HTML and is one of the reasons it pushed many other formats to the side and the web won. I would submit that HTML+JavaScript is the platform, not just HMTL. One can write declarative code in an imperative language, and the reverse is true.

I do really appreciate you thinking on this, but I think we're best to use the existing definition and example of declarative languages, and not just banish declarative to static file formats.