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by OskarS 695 days ago

Isn't the fundamental issue here not so much anything to do with `<svg>`, but with the fact that you can't easily include HTML snippets from other files in HTML? Like, the only reason not use the <svg> tag seems to be "it's not cached, and it contains a BUNCH of svg, and it has to be loaded with the main HTML page"

Can't you say that about anything in HTML? Like, imagine you had a huge `<head>` tag that contained a bunch of stuff, but it's essentially the same (except for, like, the title) for all documents. Don't you wanna do this?

    <html>
    <head>
      <<< include head.html >>>
      <title>Cool page!</title>
    </head>
    <body>
        <svg>
            <<< include logo.svg >>>
        </svg>
    </body>
    <html>

Where the `<<< include ... >>>` is a pretend bit of HTML that makes the browser fetch that from somewhere else. A preprocessor, more or less.

I realize this is what templating languages are for, but if this happened on the HTML layer, the browser could do way better caching.

9 comments

spankalee 695 days ago

There's this HTML spec issue for an include feature that I think could always use more support: https://github.com/whatwg/html/issues/2791

One of the things said in there is that they look for usage of userland solutions. I mentioned in another comment, but there are custom elements that do client-side includes, like: https://www.npmjs.com/package/html-include-element

jwells89 695 days ago

To me at least this feels like a fairly natural addition to HTML. You can already pull in external scripts, stylesheets, images, video, etc, so why not page partials too? A sibling comment mentions XSLT which is cool, but nobody knows about it because it doesn’t follow any patterns set in HTML and HTML doesn’t have any breadcrumbs that might lead someone to discover XSLT. Something like <partial src=“header.html”> flows with expectations much better.

Something I find a bit funny now is that for the longest time back in the 2000s, nearly the entirety of my usage of PHP was comprised of PHP includes to make up for this gap in HTML functionality (I had no idea XSLT existed then).

ndriscoll 695 days ago

It had breadcrumbs back in 2004 (e.g. those neat "valid XHTML 1.1" badges from W3C back when badges on your website were cool, and e.g. W3 Schools actually put it above javascript[0]. XHTML was supposed to be the next big thing). These days it seems that browser vendors just don't like it for whatever reason (tinfoil hat on: because almost all of them benefit from javascript-based spyware, and so prefer a world where even static pages require javascript to be enabled to show anything), and so documentation acts like it is some legacy thing instead of what it is: a perfect fit for the 99% of websites that need some templates and don't have much dynamic interaction.

Other cool web tech that should have "won": XForms[1]. Imagine if HTML forms had things like declarative data-binding (with XPath expressions! Imagine jq built directly into the browser 20 years ago and usable by forms) and types/constraints/validation built right in. This would be 1000x more useful for your average web dev than something like USB or GPU support or Wasm. You'd be able to make complex interactive forms in much the same way that you do a spreadsheet.

[0] https://web.archive.org/web/20040727061732/http://www.w3scho...

[1] https://www.youtube.com/watch?v=2yYY7GJAbOo

PaulDavisThe1st 695 days ago

One reason that this is slightly more complicated than it appears is that you have to decide what ignore when doing the inclusion. Including an image will not override anything specified in the "parent" HTML, but including HTML might result in conflicts. Who wins, who loses, etc. etc.

harry8 695 days ago

Why isn't it exactly the same as if the doc had the includes filled out and then processed semantically, much like C?

All <<<include whatever.html>>> could be replaced with contents first. Then it's just a page of html as now.

ndriscoll 695 days ago

HTML does have a preprocessor. It's called XSLT, and it has includes, though they have no deferred fetch. Also, being a preprocessor, you can't interact with it after page load (unless you use a javascript implementation). It's been built into browsers for 20+ years. Still works great, but browsers never supported versions past 1.0 so it shows its age some.

dspillett 695 days ago

> though they have no deferred fetch

Also, at least back when we excised the last bits of it from our old codebase, no useful caching of either stylesheets or included resources (other stylesheets), so if you tried to mix client-side processing with HTTPS you were in for quite some pain unless you had a fast, very low latency, uncongested, link.

ndriscoll 695 days ago

Currently it looks like at least Firefox and Chromium both cache stylesheets and included files as you'd expect. In fact, you can use this to increase cacheability in general. e.g. when this site is having performance issues, it often works logged out/when serving static versions of pages. It's easy to make every page static by including a `/myuser.xml` document in the xsl template and using that to get the current logged in user/preferences to put on the page. This can then be private cached and the pages themselves can be public cached. You can likewise include an `/item-details.xml?id=xxxx` that could provide data for the page to add the logged in user's comment scores, votes, etc. If the included document fails to fetch, it falls back to being empty, and you get the static page (you could detect this and show a message).

kbolino 695 days ago

XSLT is an XML transformation language, but HTML is not XML. Does XSLT work on regular HTML?

LegionMammal978 695 days ago

XSLT 3.0 can be directed to output HTML5 [0]. However, browsers only implement XSLT 1.0, and as far as I am aware there is no open-source XSLT 3.0 implementation.

Still, it's possible with XSLT 1.0 to produce documents in the common subset of XML and HTML5 ("XHTML5"). It can't produce the usual <!DOCTYPE html> at the top of the document, but it can produce the alternative <!DOCTYPE html SYSTEM "about:legacy-compat">.

On the input side, every XSLT version only accepts valid XML, as far as I am aware.

[0] https://www.w3.org/TR/xslt-xquery-serialization-30/#html-out...

o11c 694 days ago

`xsltproc --html` is an example of HTML input (probably HTML4 parsing rules though?) if you really need it. This is an XSLT 1.0 processor, wrapping libxslt which most browsers use.

As for output, the difference is largely irrelevant for browser purposes since they just want a tree.

I'm not sure how many extensions the browsers allow, but a major part of the reason XSLT 2/3 failed to take off is because libxslt already provides most of the useful features from newer versions as extensions (many via EXSLT-namespaced modules, at least partially supported in browsers - see MDN); what it doesn't do is implement the unnecessary complexity that the Java world loves.

dekhn 695 days ago

At the time HTML was converted from SGML to XML: https://en.wikipedia.org/wiki/XHTML so if you authored XHTML, you could XSLT it. There is also XHTML5, an XML serialization of HTML5. I imagine in the real world there is a great deal of web that is HTML, accepted by browser, but not XML.

kbolino 695 days ago

As far as I know, HTML5 has diverged from its origins enough that it's neither SGML nor XML. However, given the existence of XHTML5, it might be possible to parse an HTML5 DOM and re-serialize it as XHTML5, and thus it might be possible to take parseable HTML as input to XSLT, albeit with some indirection.

dspillett 695 days ago

We were going to move on to XHTML after HTML4, for those variants (did it go beyond XHTML1.1?) HTML is XML compliant. That got caught in slow design-by-committee hell though so HTML5 became the defacto standard instead. There is XHTML5 which is an attempt to direct that back towards compliance, but I've never seen it used in the wild.

ndriscoll 695 days ago

I'm not sure what you mean, but you can output HTML that a browser will be happy with, and that conforms to the spec. See e.g. https://stackoverflow.com/questions/3387127/set-html5-doctyp...

kbolino 695 days ago

As I understand XSLT, it takes an XML document as input and an XML document describing the transformation, and produces an XML document as output.

But most HTML in the wild today is not valid XML. There is XHTML as mentioned by a sibling comment but it's rarely used. So if you were to start with an existing base of HTML documents, you couldn't easily add XSLT preprocessing to them. The issue is with the input rather than the output.

nayuki 695 days ago

The fastest way to confirm that a given HTML document is not valid XML is to change the HTTP Content-Type from "text/html" to "application/xhtml+xml".

Here is what I know about using XHTML in practice: https://www.nayuki.io/page/practical-guide-to-xhtml

ndriscoll 695 days ago

If you're using it as a template language for your own pages, you can of course just write it correctly (this is not different than needing to use correct syntax for react code to compile).

If you have someone else's documents, or need to mass convert your own to fix them, there's HTML tidy[0]. This one is quite useful to be able to run XML processing CLI tools on scraped web pages.

But the real power is in delivering XML to the client, not HTML. This lets you work in the domain model directly on the frontend, and use XSLT to transform that into HTML for display. So of course you'd use well-formed XML in that case.

Imagine if you didn't have a distinction between APIs and pages; you just returned the data along with a link to a template that says how to display it and (ideally) a link to a schema definition. Modifying templates for components could be as easy as modifying CSS attributes in the browser console, giving the next generation an easy way to peak and play around with how it all works as they're growing up. We were so close, and then things veered off into the hellworld that is the modern web.

[0] https://github.com/htacg/tidy-html5

tannhaeuser 695 days ago

HTML was invented as an SGML vocabulary, and SGML does have those inclusion mechanisms (called entities), though browsers basically never implemented those. To this date, self-acclaimed web folks ridicule XML (a simplified subset of SGML originalky invented as the base for additional vocabularies on the web, of which SVG and MathMl made it) for daring to incorporate something as basic as text variables/entities ie the "billion laughs atrack" (SGML could already limit the recursive entity expansion depth).

recursive 695 days ago

We had this 25 years ago in the form of "Server Side Includes". https://en.wikipedia.org/wiki/Server_Side_Includes

You could put something like this in your markup

    <!--#include file="footer.html" -->

And the web server would apply it and inline the contents. It had a bunch of other directives, but this was the good one.

spankalee 695 days ago

A server side include wouldn't fix this problem because the SVG would be inlined everywhere. That defeats caching by duplicating the content.

Izkata 695 days ago

If we're talking just SVG, it could be done as a one-time inlining that uses <defs> to define shapes, that get pulled into the page later with <use>. The defs are page-wide and work across <svg> elements. That would fix the duplication, though not necessarily caching on its own with GP's include.

https://developer.mozilla.org/en-US/docs/Web/SVG/Element/def...

nbadg 695 days ago

I think whether or not this makes sense on the client-side is up for debate.

Alternatively, though, SVGs in ``<svg>`` elements could just, yknow, retain their stylability. (is there a reason they don't? this has been a long-running frustration of mine)

cubefox 695 days ago

You mean <img>. <img> is not stylable.

danbee 695 days ago

Turbo Frames (https://turbo.hotwired.dev/handbook/frames) does this. It does mean pulling in a JavaScript library (and the user having JS enabled) but you don't have to write any.

I'd definitely love to see something like this built into the browser.

panstromek 695 days ago

Yes, I want this and it would solve quite a few issues - particularly lazy loading and SPA-style content swapping could be done with better performance, because html can be easily processed and rendered during download by the browser (unlike the classic AJAX -> Json.parse -> render pipeline, which requires each step to be completed before the next one starts). Lazy loading would also not require JavaScript.

tracker1 695 days ago

I may be completely off and/or misremembering, but isn't this what <object> was meant to be able to do/support? Seems that this could be done by convincing Apple/Google/Firefox to reframe/update how the object element works in modern browsers.