What error are you getting on the site? If you are talking about W3C validation, it doesn't matter to me. What matters is that the site works. No normal site passes W3C validation (google.com, microsoft.com, apple.com, yahoo.com, facebook.com, twitter.com, etc.)
Because it doesn't affect user experience or anything else. The better question I think is why *does* it matter for you?
No problems here either. What W3C says does not really matter at all. Browsers are no longer strict like they use to me. It's kinda like saying you have to use 100% proper English to be understood. You don't.
As you said yourself, there are no errors here. You are relying on a third-party site to tell you if you have errors based on their own criteria. The only relevant errors are ones you encounter when on the site in question. If W3C mattered whatsoever, don't you think websites like Google, Apple, Microsoft (the companies who make browsers even) would follow W3C guidelines? If you look at the "about" page for the W3C validator, the intended purpose of the validator is to help site owners catch unintended mistakes, it doesn't have an intended purpose of helping people pass validation 100%. https://validator.w3.org/nu/about.html There are no unintended mistakes on our main webpage (at least not ones that W3C brought to light). Again, the only relevant errors for our site are ones that happen on our site.
Where do you see that? If you go here, and search for the word "mistake" they don't even have that word on the page. https://validator.w3.org/nu/?doc=https://www.digitalpoint.com/ Either way, until there are errors *on* our site, we aren't going to try to confirm to the standards of some governing body that has no relevance for user user experience. I highly doubt there's *any* major site that passes their validation tool checks. It's one of those things where if you are super bored and add extra markup to your site (which in turn makes it slower) so you can have a warm and fuzzy feeling that W3C thinks you are swell, by all means... go for it.
LOL, I know it doesn't say mistake, but it says error. the w3c established the html standards like html4 and html5.
Yep... But browser compatibility is more important that "perfectly" formed HTML when I comes down to it.
The strict check for HTML 5 gives you errors that shouldn't be errors to begin with - for example if you use "screen, projection, tv" on the stylesheet-link (projection and tv are deemed unnecessary and has been deprecated in HTML 5) - other things that gives errors (sometimes) are the use of placeholders, some data-types on input (which doesn't matter - if the browser doesn't support said type, it just defaults to text) and so forth and so on. The validator has less and less meaning, unfortunately. 10 years ago, it actually did good, and a site that conformed 100% usually had at least working markup and some kind of understanding. Today, there are plenty of garbage sites that could, in theory, pass validation, without having proper markup (look at bootstrap-based sites, for instance). The point is: some of the errors reported by the validator SHOULD matter, and should be fixed. Those are things like duplicate IDs, missing closing elements, missing headings, elements without parent elements, and so on. Those should all be fixed. Knowing what errors doesn't really matter is part of learning to code properly.
Back when sites were hand coded it was a useful tool to see what we'd missed. I'm not sure I ever got a site down to 0 errors but there was definitely the expectation that the list should be really short. With the use of third party scripts (Xenforo, WordPress) we no longer have control over the production of a site and it won't be appropriate to go delving into the code to make fixes because they'll need to be repeated with every upgrade. Add to that the user generated content (like this post) and you are losing a bit more control. Here's an image - but it won't have alt tags because I've just copied and pasted it into the post - it was never even a file. Now the forum could demand I put one in but that reduces the user experience and makes me less likely to contribute. Edit: the forum gives it a basic alt tag but to be really useful it should be provided by the user. There are users on here who make a big deal about the validator but it's a bit like a vegan eating honey. The odd minor slip up isn't the end of the world.
And the wysiwyg editor is provided by tinymce. It's a good editor, one of the best out there, but it's so not easy to customize.