XML is really great for text documents with embeds and markup, either semantic (this part of the paper is an abstract) or visual (this part of the document should be 14-point and aligned right). You can do this in JSON, but it's a pain.
JSON is great for representing data. If you have some data structures and two machines trying to exchange them, JSON is great for that.
TOML / yaml / hcl / JSON with comments are great at config. If you have a human writing something that a machine is supposed to understand, you don't want turning completeness and you don't want to deal with the pain of having your own DSL, those are great.
HTML is actually a dialect of SGML. XHTML was an attempt to move to an XML-based foundation, but XML's strictness in parsing worked against it, and eventually folks just standardized how HTML parsers should interpret ill-formed HTML instead.
Ah good to know. It’s interesting (to me) how similar they look to each other but you and other commentators below mention how they’re more like distant cousins
No, HTML was historically supposed to be a subset of SGML; XML is also an application of SGML. XHTML is the XML version of HTML. As of HTML5, HTML is no longer technically SGML or XML.
HTML is far loosier-goosier in its syntax than XML allows. There was an attempt to nail its syntax down in the pre-HTML 5 days; that's XHTML. When HTML 5 pivoted away from that, that spelled the end of these two things ever coming together.
Really, I think you can trace a lot of the "XML is spooky old technology" mindset to the release of HTML 5. That was when XML stopped being directly relevant to the web, though of course it still lives on in many other domains and legacy web apps.
> There was an attempt to nail its syntax down in the pre-HTML 5 days; that's XHTML. When HTML 5 pivoted away from that, that spelled the end of these two things ever coming together.
Exactly the opposite; WHATWG “Living Standard” HTML (different releases of which were used as the basis for W3C HTML5, 5.1, and 5.2 before the W3C stopped doing that) includes an XML serialization as part of the spec, so now the HTML-in-XML is permanently in sync with and feature-matched with plain HTML.
“Warning!
Using the XML syntax is not recommended, for reasons which include the fact that there is no specification which defines the rules for how an XML parser must map a string of bytes or characters into a Document object, as well as the fact that the XML syntax is essentially unmaintained — in that, it’s not expected that any further features will ever be added to the XML syntax (even when such features have been added to the HTML syntax).”
No, HTML was a specific application profile of SGML (modern HTML, I believe, no longer technically is), XML is a newer (than HTML) application profile of SGML inspired by HTML but aiming for greater generality.
XHTML was an attempt to encode HTML semantics (approximately, each version of XHTML also altered some semantics from HTML and previous XHTML versions) in XML, and the XML serialization of modern, WHATWG HTML exactly encodes HTML semantics in XML.
Yes, there's a handful of niches. Still 1/1000th the momentum it had, or adoption it was expected to get, and nobody under 40 even considers it for new stuff.
