what is the point of being XHTML compliant?

All modern browsers understand HTML, so what is the point of being XHTML compliant other then writing more 开发者_StackOverflow社区characters found on the far right side of the keyboard.

There is no point that I can think of. The W3C has canceled XHTML 2.0, although there is supposed to be an XHTML5, which I guess is HTML5 for masochists. Originally XHTML was going to lead us into the world of "correct" HTML documents, but it generated as many (or more) problems than it ever solved.

We validate against either HTML 4.01 Transitional or HTML5 (to the degree that you can do that). That plus clean CSS gives you about the best you can shoot for.

XHTML was originally supposed to be a "next generation of HTML", as well as a stricter version of HTML (which would cause failures if any error showed up in the page). Due to a variety of loopholes and any number of other issues with XHTML (such as pages serving up the wrong mimetype), hardly any pages are actually XHTML, they're just HTML with some extra characters.

Eventually, HTML5 was proposed, w3c split into two groups, then the people working on XHTML 2.0 switched to something better (HTML5) and now everyone is talking about HTML5 taking over everything.

For a longer version (with far more detail), check out this chapter from Dive Into HTML5: http://diveintohtml5.ep.io/past.html

According to http://www.dev-archive.net/articles/xhtml.html, one of the reasons XHTML was created was:

to add the XML ability to extend the language through namespaces. This will make it possible for an author to express more structures and richer semantics than is possible with HTML today. In effect XHTML inherits the possibility of supporting more than one language — instead of extending HTML in a monolithic fashion, XHTML can be extended through modules, where each module define a specific subset of the language.

This, theoretically, means extension of the language can be done without the need for a browser upgrade.

XHTML is meant to make the use of XML–based languages in end–user applications such as browsers easy, but can also be used for various data processing and storage purposes in situations where the web is only one of several channels. XHTML take advantage of the extensibility of XML to support multiple namespaces and through them languages.

That article also notes that for most people this won't be useful:

Recommendations

If you don’t have any specific need to deliver XML–based structures to the client, e.g. due to mixing namespaces such as having MathML content in your pages, using Ruby (XHTML 1.1) or techniques such as ACCESS (XHTML 1.2) then consider whether you won’t be better off simply by using HTML 4.01 Strict.

Edit with additional thoughts:

I forgot to mention the point I popped in here to bring up too - XHTML can be more easily manipulated into other languages using XSL transforms.