Standards-compliant sites are sites which conform to the X/HTML specification declared in the doctype, and the W3C CSS spec, as far as I'm concerned. The accessibility specs are too vague and inaccurate to really be considered a measurable standard, and your points #2 and #3 are really arguable, it depends what school of design you come from. There is nothing in the spec that mandates relative text sizing, and many professional web developers feel (i'm one of them) that this should be the browser's domain (see IE7 / Opera's zoom functionality). I personally go for CSS for all presentation, and this is indeed the standard for XHTML, but it's perfectly possible to build HTML 4 documents using HTML attributes for some styling.

Definitely has to pass the validator at W3C and have valid CSS. Anything else is irrelevant regarding compliance with the standards. Item number one in your list will be covered if the markup passes the validator as it is required. Item two is the goal of future specs, seperating content from layout. Currently mixing is allowed but many designers think keeping them seperate is good design and the only way to do it. The third item is a function of accessability. One way to allow this as gracefully as possible is to use ems and not override a users CSS with !important.

As far as what anyone would add, I would kill the moron that invented flash. Talk about inaccessability!

I would add:

* Valid XHTML & CSS markup, including properly nested and closed tags

* Avoidance of presentation-type tags, such as tables, when not presenting tabular data

* Clear separation of markup of content from design presentation (similar to your rule #2)

* Ability for site to be fully used (minus obvious media limitations, such as sound or video) on a text-based browser or reader for the blind.

Well for starters, I always get a kick out of how these conversations go. You try to have an interesting discussion with web programmers by asking an open question and at least a few of them will always reply with something to the effect of "here's the one and only answer, problem solved."

I think that "standards-compliant" is generally interpreted to mean w3c compliant, but that the points made about presentation and accessibility are good ones as well. But there's standards and then there's standards:

1. something considered by an authority or by general consent as a basis of comparison; an approved model
2. those morals, ethics, habits, etc., established by authority, custom, or an individual as acceptable

There's always the great vague fog of "web standards" that tend more towards philosophy. Accessibility is part of that. I try to write my sites as screen-reader-friendly as possible, though I admit I haven't been using relative font sizes. Mostly that's just because I haven't bothered to troubleshoot them and establish a personal standard (definition 1). My current goal is to become an expert at using CSS to design wap-friendly sites. Anyway, I think my guiding principles are the following:

-Accessibility (screen readers, relative font sizes, wap alternatives)
-Graceful degradation
-Separating content from layout
-Usability (good UI and a minimum of annoying crap--sorry <blink>)
-Minimalism, flexibility and reusability of code

The last is definitely a personal tic. I'm a clean-freak. And I was raised by German engineers. I like things to be efficient, to do exactly their job and no more, and a minimum of redundancy.

Anyway. I think all that stuff's fun to talk about too. Otherwise what is this tribe for? W3C standards and browsers that blow them off. Let me tell you how much I hate Mac Netscape 7...

I have to agee with david here. When we say "Standards Compliant" as a feture or build spec of a site it means just that - compliant with the standard for its xhtml/html doctype (and keep in mind this is going to vary) and the CSS specification. Thats all it means, thats all it can mean.

Now as Kelly kind of got in to, on top of that designers and developers have thier own sets of personal/wrokgroup/etc.. standards that may be layerd on top of that - and thats just fine. Now on top of that you may be required to adhere to some sort of accessibility specifications (which may or may not be the ones crafted by the w3c workgroup), but thats not necessarily part of being "standards compliant". thats a whole other issue. Same thing with relative font sizes... thats a philosophy/best practice/goal of certain elements of the design/development/usability community but it has nothing to do with being standards compliant - using pt or px measurements for type isnt going to get fialing grade in a validator.

i wonder why nobody mentioned RSS yet?
i haven't been using it myself first but now it's hard to me to imagine using internet without syndication.
IMHO every non-static website should have RSS feeds implemented! (as a standard)