It’s ironic that the very site in question, despite claiming XHTML compliance, is served as text/html instead of application/xhtml+xml, so the browser will never parse it as XML.
To quote [0]:
> All those “Valid XHTML 1.0!” links on the web are really saying “Invalid HTML 4.01!”.
Although the article is 20 years old now, so these days it’s actually HTML5.
Edit: Checked the other member sites. Only two are served as application/xhtml+xml.
That HTML5 was used in marketing doesn't make the technical term disappear. HTML5 is a bit more precise than HTML, it refers to the living standard that's currently in use, as opposed to HTML 4.01 and the previous versions of HTML.
It's not a technical term. Nowhere in the current HTML standard will you find a versioning of HTML. That's why it's now called a "living standard". You will never find a HTML6 or higher. That note you found is to help with any confusion.
You might be right, but we don't know yet. Microsoft said that for Windows 10.
You might also be right that the current Living Standard specification doesn't really call it HTML5, but you'll find many people writing HTML for a living say HTML5 to refer to it, and telling them that HTML5 doesn't exist doesn't really help and is a bit wrong too if you have a descriptive approach to languages.
The next version of html should be able to do all the http verbs -- get, put, patch, post, delete online, reactively without having to use a form.
There has to be a way to figure this out, even if it requires a transition period. The best time to plant a tree was twenty years ago, the second best time is now. These things belong in the core HTML standards, not a js library you need to include in your code.
Oh that and better controls and better defaults but I guess that is something individual web browsers can implement on their own?
Telling them HTML5 does exist does even more harm cause it doesn't exist. Telling them it does exist is entirely wrong and is even a false statement, is misleading and causes confusion.
One of the annoying things about having a living standard is that it is difficult to implement a conforming version as additional updates means that you are no longer conforming.
Versioned standards allow you to know that you are compliant to that version of the specification, and track the changes between versions -- i.e. what additional functionality do I need to implement.
With "living standards" you need to track the date/commit you last checked and do a manual diff to work out what has changed.
I used to create a number of simple web pages in XHTML back in the days when we believed XHTML was the future. Recently, while going through and restructuring some of my old "online stuff", I learned that XHTML really isn't in a state that I'd want to use it any more:
* XHTML 1.0 and 1.1 are officially deprecated by the W3C.
* XHTML5 exists as a variant of HTML5. However, it's very clear that it's absolutely not a priority for the HTML5 working groups, and there's a statement that future features will not necessarily be supported by the XHTML5 variant.
* XHTML5 does not have a DTD, so one of the main advantages of XHTML - that you can validate its correctness with pure XML functionality - isn't there.
* If you do a 'view source' in Firefox on a completely valid XHTML 1.0/1.1 page, it'll redline the XML declaration like it's something wrong. Not sure if this is intended or possibly even a bug, but it certainly gives me a 'browser tells me this is not supposed to be there' feeling.
It pretty much seems to me XHTML has been abandoned by the web community. My personal conclusion has been that whenever I touch any of my old online things still written in XHTML, I'll convert them to HTML5.
> If you do a 'view source' in Firefox on a completely valid XHTML 1.0/1.1 page, it'll redline the XML declaration like it's something wrong
Is the page actually being served as "application/xhtml+xml"? Most xhtml sites aren't, in which case the browser is indeed interpreting those as invalid declarations in a regular old html document
Those red squiggles on view-source: pages in Gecko all have title text with diagnostics. The message (errProcessingInstruction) in recent-ish releases is given as:
> Saw “<?”. Probable cause: Attempt to use an XML processing instruction in HTML. (XML processing instructions are not supported in HTML.)
I was in college when XHTML was all the rage and everything we wrote had to pass validation. I still get uncomfortable adding breaks without closing them.
There used to be a commenter here who would end all his comments with a closing paren, even though there had not been an opening paren. It led to a surprising number of flamewars! )
Edit: hmm, I couldn't really find any flamewars, but it did lead to objections:
Hilarious. To fix this, one would have needed to put an open parenthesis in a sibling comment and hope to get upvoted more than the comment with the closing parent.
XHTML survives in ePub. Recently there was a survey to gather industry feedback for a potential addition of an HTML flavour of ePub to be added to the next version of the spec, but it soon became fairly clear that people saw a lot of value in remaining XHTML-only: https://www.w3.org/blog/2026/epub-and-html-survey-results-an...
I highly recommend everyone involved in web development to read at least a small proportion of the horrors that are the HTML parser specification. It will leave you yearning for the return of XHTML.
Or you could also read web proposals where the reason for avoiding the ideal implementation is complication of updating HTML parser rules.
Or attempt to use the web features that are already hindered by the HTML parser (custom element table rows).
Grateful in part, but I can't help to think that if there was refusal to build parsers for an outlandish spec in the first place then we'd have fixed the problem by now.
Using existing parsers only hides the poor design up to a point.
I mostly agree with the sentiment, I'd rather have simple parsers and sensible specs, but I'm also happy they do whatever it takes not to break anything (well, they are breaking XSLT…)
I would really like to use XHTML. It would make my HTML emitter much simpler (as I don't need special rules for elements that are self-closing, have special closing or escaping rules and whatever else) and more secure.
However no browsers have implemented streaming XHTML parsers. This means that the performance is notably worse for XHTML and if you rely on streaming responses (I currently do for a few pages like bulk imports) it won't work.
> no browsers have implemented streaming XHTML parsers
Dang, I hadn't considered this. That's something to add to the "simplest HTML omitting noisy tags like body and head vs going full XHTML" debate I have with myself.
One for XHTML: I like that the parser catches errors, it often prevent subtle issues.
> you should master the HTML programming¹ language
The footnote reads:
> 1. This is a common debate - but for simplicity sake I'm just calling it this.
It's not really a debate, HTML is a markup language [1], not a programming language: you annotate a document with its structure and its formatting. You are not really programming when you write HTML (the markup is not procedural) (and this is not gatekeeping, there's nothing wrong about this and doesn't make HTML a lesser language).
To avoid the issue completely, you can phrase this as: "you should master HTML" and remove the footnote. Simple, clean, concise, clear. By the way, ML already means "Markup Language", so any "HTML .* language" phrasing can feel a bit off.
Of course HTML is a programming language. It's one of the languages I use every day to program with. I'm not sure what the definition of a programming language would be beyond that.
Do you mean "Turing-complete" language? Or maybe "procedural programming language"? I agree HTML isn't either of those, but those aren't the be-all and end-all of programming now, are they?
I, and most of us, mean a language in which one can express a computer program, which is a set of instructions for a computer to execute. You don't execute an HTML file, you display it, render it. You can't implement fizz buzz in HTML. At best, you mark up its output. With HTML, you don't instruct, you describe. You instruct what to do with JavaScript, or Python, or whatever programming languages you use client or server side.
A programming language doesn't need to be procedural, it can be functional, or use another computationally equivalent paradigm. I'm not quite sure it needs to be Turing complete, but possibly.
A programming language lets you express to some processor that provides a set of computation primitives what to do with the memory cells you have at your disposal, and in general it lets you deal with input and output.
If you consider any language you program with to be a programming language, then CSS, JSON, YAML, XML, markdown (that's what your readme is likely written in) and even English (that's what you use to express the specs, the bugs, maybe your notes / drafts, the comments, possibly the language the singer of the songs you're listening to while programming use) or UML need to be programming languages too. That's not quite useful. "Program with" is too large and would make the "programming" qualifier largely useless.
An HTML file is a set of instructions to execute. They're very high-level, declarative instructions for describing a UI, similar to how SQL is high-level declarative instructions for describing a set of data to be loaded, or how Prolog is a high-level declarative set of instructions for describing a set of logical axioms, but they're still instructions. You pass them to an execution engine, and on the basis of the instructions you've written, the engine does something. (See e.g. the section on fourth generation PLs in the second link you gave.)
More broadly, I think this discussion is a stupid one. There is no formal, mathematically precise definition of a programming language. There are formal definitions of lots of PL-related things, and for what a language is in general (a combination of syntax and semantics), but there's no formal definition of the term "programming language" that's useful here.
So if we're not arguing about a formal definition, then we're arguing about essentially our favourite dictionaries, and how we personally interpret our favourite dictionaries. And that's just not a useful argument at all, it's not even how dictionaries are meant to work! And yet whenever someone dares to write "HTML programming language" or something similar, there is always a comment from someone demanding that the author use their personal dictionary, and correct their changes. And it is deeply grating, because whenever I see this happen:
* The original statement is never ambiguous. I have never seen a situation where referring to HTML as a programming language has ever caused some sort of confusion.
* The discussion about whether HTML is a programming language is almost always completely irrelevant to the topic at hand, and bringing it up adds no value to the discussion.
* The author's definition is usually inconsistent anyway. Which isn't a problem — I don't imagine my mental definition of a programming language is entirely consistent either — but it's dumb watching someone try and correct other people without understanding their own definition enough to be able to respond to clarifying questions.
In your original comment, you said "it's not really a debate", and that's completely correct. It's not a debate because there's no right answer. There's not even any value to a right answer. The matter is entirely a question of terminology. And if different choices of terminology make things unclear, then it might be worth clarifying that terminology, but here I don't think the author could have been any clearer at all about what they were trying to communicate.
> More broadly, I think this discussion is a stupid one
Mostly agree (although reasoning about these things can be interesting). More on this at the end of the comment.
> So if we're not arguing about a formal definition, then we're arguing about essentially our favourite dictionaries
It's also a matter of the most widely accepted definitions, not just what definition one prefers. And it seems to me not considering HTML as a programming language is what's most accepted and for good reasons.
We need a common understanding to communicate.
> I don't think the author could have been any clearer at all about what they were trying to communicate.
They just make their expression more confusing and more complicated by needlessly qualifying HTML and putting this footnote when they could have skipped both the footnote and the qualifier.
Here I was in fact mostly concerned about the clarity and the presentation. That page seems to be written for newcomers, qualifying HTML as a programming language doesn't seem quite optimal given the (supposed) target, I think it would do a disservice to someone who has not a great understanding of those things.
So the better way of exposing things IMHO is just not mentioning it at all, and if someone wonders whether HTML is a programming language, they can do their own research.
> An HTML file is a set of instructions to execute
I believe it's a stretch to describe HTML like this. Your explanation makes it work, but I don't think it's a usual way of viewing HTML. In any case it seems to me presenting HTML like a set of instruction to execute to a newcomer would just be weird.
Now, this discussion wouldn't matter much between people who have such a clear understanding of these things as you. When everything is this clear, deciding whether HTML is a programming language is indeed a purely intellectual exercise that can totally feel pointless and where both positions are probably reasonable depending on the perspectives, and yes, on the exact, clarified definition one uses.
So I was wrong: there is a debate. It was incautious of me to state otherwise. And the debate is mostly pointless for whoever clearly understands the involved concepts. And I should have focused on the pedagogical aspect of this stuff, not on whether it's wrong.
I will definitely handle such a discussion differently next time, if I don't outright skip it.
What happens if I simply add an iterator mechanism to HTML (well, I guess we need variables too)? Is it no longer a markup language here (I won't add anything else):
<for i=0; i<1; i++>
<html>
</html>
</for>
Better question, why don't we upgrade XML to do that?
But if you disagree with this, or somehow work around this statement by replacing your for element with some "for-loop" custom element (it is valid HTML to add custom tags with dashes in their names), my stronger argument is at https://news.ycombinator.com/item?id=46743219#46743554
I ask you then: (1) how do you deal with the template that surrounds a large number of pages on a site? (2) how do you deal with the fact that the average web form might want to display something different based on the form contents (e.g. redraw the form if there's an error, draw something different on success?) (3) do you write anything that returns JSON or other results for AJAX or web services?
If HTML was never able to be the full solution, then I guess if I had to expand on where I'm going, then what the heck are we even doing with this html thing? Either MAKE IT like PHP, ditch it, or do something, anything.
HTML is perfectly able to do what it was designed for: mark up documents.
There still needs to be something like HTML even when you have PHP: PHP is something you run on the server and it still needs to output something to the client in some format, and HTML is adequate for this.
The heck we are doing with HTML is taking it for building client apps. But even then, you now have UI toolkits that mimic this model: QML, whatever XML format Android has to design UIs, etc.
> Either MAKE IT like PHP, ditch it, or do something, anything.
Do nothing so I can make websites that are accessible, secure, static and fast. HTML is the full solution unlike PHP or JS. With CSS it’s Turing complete.
I dunno, you're being pedantic :) Yes yes, the name clearly ends up "Markup Language" so yeah, with a very strict definition of programming languages, HTML is not one of them.
But if we use a broader definition, basically "a formal language that specifies behavior a machine must execute", then HTML is indeed a programming language.
HTML is not only about annotating documents or formatting, it can do things you expect from a "normal" programming language too, for example, you can do constraints validation:
That's neither annotating, just a "document" or just formatting. Another example is using <details> + <summary> and you have users mutating state that reveals different branches in the page, all just using HTML and nothing else.
In the end, I agree with you, HTML ultimately is a markup language, but it's deceiving, because it does more than just markup.
It might be, I'm usually not, but this is all xhtml.club and this footnote are about, might as well be correct :-)
Constraint validation is still descriptive (what is allowed)
All details and summary are doing is conveying information on what's a summary and what's the complete story, and it has this hidden / shown behavior.
In any case, you will probably find something procedural / programming like in HTML, but it's not the core idea of the language, and if you are explaining what HTML is to a newbie, I feel like you should focus to the essential. Then we can discuss the corners between more experienced people.
In the end, all I'm saying is: you can just avoid issues and just say "HTML" without further qualifying it.
This is not what HTML does. Tags are not instructions, they delimit the start and end of elements. They describe content, they do not specify behaviour.
In your pattern example, that is still just a description of what is acceptable input. It doesn’t execute anything. A paper form might specify the format DD / MM / YYYY but that doesn‘t mean the form is executing a program in your brain when you fill it out.
I'm not sure we can call your parent comment pedantic. They're just being correct. Is it pedantic to say that fish is not a fruit? It's just correct to do so.
If anything, it is the act of stretching the definition of "programming language" so much that it includes HTML as a programming language that we should call pedantic.
One threshold is "can you write a program that might not complete?" You can't in SQL, which makes it less of a programming language than, say, FORTRAN.
If you look at the HTML 5 spec it is clear that it's intended to be a substrate for applications. The HTML 5 spec could be factored into a specification of the DOM, specification of an x-language API for the DOM and a specification for a serialization format as well as bindings of that x-language API to specific languages like Javascript.
Back when it was fashionable to complain about how every Electron application has 30 MB of bloat I did an eval of all the options for x-platform applications that weren't Electron and came to the conclusion that "they all sucked" except for maybe JavaFX -- and not everybody likes Java as much as I do.
Building up to Win 8, Microsoft pushed for grid and flexbox which are the bees knees for laying out applications in HTML.
Compare the annoying nag dialogs in MacOS and Windows. MacOS nags you to buy into Apple Music and other unwanted services with 2025 reskins of the 1999 reskins of the modal dialogs from the 1984 Mac Classic. Windows does the same with ads that look like advertising which I find more visually appealing even if the services are unappealing.
Every time I think about writing a GUI application that's not a web application I think "this is a waste of time" whereas my web applications keep finding new lives as mobile applications, VR applications, etc.
> Back when it was fashionable to complain about how every Electron application has 30 MB of bloat
What, it's not anymore??
And yes, I do end up writing web applications every time too (I haven't bundled them though). I don't want to tie myself to a specific platform, and being able to point users to an URL and bam, they can run the thing, is convenient. I hate that this makes me dependent on tech maintained with Big Tech money though.
I think that it is a debate, and it depends on the role of HTML in your system.
If all you're doing is using HTML to "annotate a document with its structure and its formatting", then yes, I'll accept that it's not quite programming, but I've not seen this approach of starting with a plain non-html document and marking it up by hand done in probably over two decades. I do still occasionally see it done for marking up blog posts or documentation into markdown and then generating html from it, but even that's a minuscule part of what HTML is used for these days.
Your mileage my vary, but what I and people around me typically do is work on hundreds/thousands of loosely coupled small snippets of HTML used within e.g. React JSX, or Django/Jinja templates or htmx endpoints, in order to dynamically control data and state in a large program. In this sense, while the html itself doesn't have control flow, it is an integral part of control flow in the larger system, and it's extremely likely that I'll break something in the functionality if I carelessly change an element's type or attribute value. In this sense, I'm not putting on a different hat when I'm working on the html, but just working on a different part of the program.
Those are not HTML. PHP neither, even when used as a templating language for HTML.
> htmx endpoints
Not really familiar with htmx, but I would say this is HTML augmented with some additional mechanisms. I don't know how I would describe this augmented HTML, but I'm not applying my "not programming" statement to htmx (I probably could, but I haven't given enough thoughts to do it).
> In this sense, I'm not putting on a different hat when I'm working on the html, but just working on a different part of the program.
I agree with this actually. I wouldn't consider that writing HTML (or CSS) is really a separate activity when I'm building some web app.
> In this sense, while the html itself doesn't have control flow, it is an integral part of control flow in the larger system
That's correct but I don't see what it has got to do with the question of whether HTML is a programming language or not.
Strings do not have control flow but strings are integral part of larger programs that have control flow. So what? That doesn't make strings any closer to being programming languages.
It's a question of semantics. What I'm saying is that the way many of us use html in practice in 2026 is less like arbitrary strings and more like db connection strings, where most of our focus is not on whether a bit of text is an article or an aside, but about how it participates in the control flow across different components in our architecture.
From another perspective, I'm not familiar with any present day company, where the html they use in their source code is sufficiently simple and distinct from the rest of the program to be managed by non-programmers. The only html that is just used as strings is that used for individual posts in a crm or marketing tool's cms, typically stored in a database rather than the source code repository.
> Validation is ignored, and most modern sites are built with little concern for structure or longevity.
I remember going online with a modem in the 90s. There was a new ISP in town, but their homepage took forever to load. I viewed the source, and whatever page generator they were rendered the page as HTML tables (this was fine back then), and added repetitive style tags to every table cell instead of using CSS (although I wonder if this was before CSS) or not doing so for empty cells, and that their homepage was so bloated and slow to load on dial-up.
I wonder how it is nowadays. But I suppose in the age that accomodates apps like Teams and Slack, who cares?
> whatever page generator they were rendered the page as HTML tables (this was fine back then), and added repetitive style tags to every table cell instead of using CSS
Apart from the fact that very few people understood CSS back then, there was a stupendous amount of really weird bugs. For instance, I remember having a simple th { font-size: … } rule, and some versions of Netscape 4 somehow managed to apply the font size to all <th> cells except for the third one. So workarounds like extra style attributes were added to fix things like this.
I don’t thing it’s about luddites as website mentioned. Many professions have tools suggesting that person have extensive experience and in terms of web development, XHTML 1.0 or old standards of HTML are such.
It is not “your HTML”, it’s HTML 4.01 from 1999, when XHTML 1.0 is from 2000. The common is the origins of validations that comes from W3 validator (1).
In the early 2000s I was 100% sold on the idea of strict XHTML documents and the semantic web. I loved the idea that all web pages could be XML documents which easily provided their data for other sources. If you marked your document with, an XHTML 1.0 Strict or XHTML 1.1 doctype, a web browser was supposed to show an error if the page contained an XML error. Problem was, it was a bit of a pain to get this right, so effectively no one cared about making compliant XHTML. It was a nice idea, but it didn't interact well with the real world.
Decades later, I'm still mildly annoyed when I see self-closing tags in HTML. When you're not trying to build a strict XML document, they're no longer required. Now I read them as a vestigial reminder of the strict XHTML dream.
As someone who has gotten into the idea of semantic Web long after XHTML was all the rage[0], I somewhat resent that semantic Web and XML are so often lumped together[1]. After all, XML is just one serialisation mechanism for linked data.
[0] I don’t dislike XHTML. The snob in me loves the idea. Sure, had XHTML been The Standard it would have been so much more difficult to publish my first website at the age of 14 that I’m not sure I would have gotten into building for Web at all, but is it necessarily a good thing if our field is based on technology so forgiving to malformed input that a middle school pupil can pass for an engineer? and while I do omit closing tags when allowed by the spec, are the savings worth remembering these complicated rules for when they can be omitted, and is it worth maintaining all this branching that allows parsers to handle invalid markup, when barely any HTML is hand-written these days?
[1] Usually it is to the detriment of the former: the latter tends to be ill-regarded by today’s average Web developer used to JSON (even as they hail various schema-related additions on top of JSON that essentially try to make it do things XML can, but worse).
That is a good point, if you consider XSD then that is an XML connection, it starts to become a bit complicated and I see why people start to dislike it. I forget about that because to me it’s just about the idea of a graph, which is otherwise quite elegant. Why not have a graph type-free with just string literals; much richer information about what kind of values go where can be provided through constraints, vocabularies, etc.
My favourite serialisation has got to be dumb triples (maybe quads). I don’t think writing graphs by hand is the future. However, when it comes to that, Turtle’s great.
Because the semantics of numbers and dates matters.
It's absurd that JSON defines numbers as strings and has no specification for dates and times.
I believe we lose a lot of small-p programming talent (people who have other skills who could put them on wheels by "learning to code") the moment people have the 0.1 + 0.2 != 0.3 experience. Decimal numbers should just be on people's fingertips, they should be the default thing that non-professional programmers get, IEEE doubles and floats should be as exotic as FP16.
As for dates, everyday applications written by everyday people that use JSON frequently have 5 or more different date formats used in different parts of the application and it is an everyday occurrence that people are scratching their heads over why the system says that some event that happened on Jan 24, 2026 happened on Jan 23, 2026 or Jan 25, 2026.
Give people choices like that and they will make the wrong choices and face the consequences. Build answers for a few simple things that people screw up over and over and... they won't screw up!
> Because the semantics of numbers and dates matters.
Type semantics is only a small part of what is needed for systems and humans to know how to adequately work with and display the data. All of that information, including the type but so much more, can be supplied in established ways (more graphs!) without having to sprinkle XSD types on your values.
For example, say you have a triple where the object is a number that for whatever good reason must lie between 1 and <value from elsewhere in the graph> in 0.1 increments. Knowing that it is a number and being able to do math on it is not that useful when 99% of math operations would yield an invalid value; you need more metadata, and if you have that you also have the type.
Besides, verbatim literal, as obtained, is the least lossy format. The user typed "2.2"—today you round it to an integer but tomorrow you support decimal places, if you keep the original the system can magically get more precise and no one needs to repeat themselves. (You can obviously reject input at the entry stage if it’s outlandish, but when it comes to storage plain string is king.)
You're annoyed when people are trying to keep the dream alive?
Since HTML5 specifies how to handle all parse errors, and the handling of an XML self-closing tag is to ignore it unless it's part of an unquoted attribute value, it's valid HTML5.
I'm not annoyed by it when people are trying to make XML compatible documents, but effectively no one is. Platforms like WordPress use self-closing image tags everywhere, but almost no one using WordPress cares about document validation. This ends up meaning that the `<img ... />` is just an empty gesture.
Circa '99 a high fraction (50%-ish) of HTML in the field was invalid, so if you were making a new web browser it had to parse invalid HTML the same way as Netscape which was one more reason we didn't get competitive web browsers.
HTML 5 specified exactly how "invalid" HTML is parsed so now there is no such thing as invalid HTML. XHTML was one of those things that never quite worked:
The things that are invalid should all have defined behaviour. For example, a <label> is not allowed to contain two form controls, but is defined as applying to the first such control.
> This specification defines the parsing rules for HTML documents, whether they are syntactically correct or not. Certain points in the parsing algorithm are said to be parse errors. The error handling for parse errors is well-defined (that's the processing rules described throughout this specification), but user agents, while parsing an HTML document, may abort the parser at the first parse error that they encounter for which they do not wish to apply the rules described in this specification.
The idea of almost all of HTML’s errors (parsing and conformance) is that they indicate likely errors (though it’s definitely quite possible to deliberately skirt the edges, e.g. content=width=device-width,initial-scale=1).
To quote [0]:
> All those “Valid XHTML 1.0!” links on the web are really saying “Invalid HTML 4.01!”.
Although the article is 20 years old now, so these days it’s actually HTML5.
Edit: Checked the other member sites. Only two are served as application/xhtml+xml.
[0]: https://webkit.org/blog/68/understanding-html-xml-and-xhtml/