Fedora and fallback DNS servers [LWN.net]

Fedora and fallback DNS servers

Posted Feb 25, 2021 18:49 UTC (Thu) by NYKevin (subscriber, #129325)
In reply to: Fedora and fallback DNS servers by excors
Parent article: Fedora and fallback DNS servers

> (virtually everyone sent it with Content-Type: text/html which meant it got parsed as HTML4 instead, relying on the browsers' error handling to cope with e.g. " " which is not valid HTML4)

To clarify: That technically *is* valid HTML4, it's just the wrong HTML4. Formally, it's equivalent to > (i.e. the tag ends at the slash, as part of a more general <foo/bar/ syntax which is allegedly "easier" than writing <foo>bar</foo>), but I think approximately three people in the entire history of the universe have actually wanted it to be interpreted that way, so all the browsers cheated and ignored the slash. Then XHTML came along and said "actually, you need the slash" and made everything even worse (because as you say, everyone was serving XHTML with text/html and it was then getting parsed as HTML4).

Then HTML5 came along and had to fix this mess. So they decided to specify that the slash is optional and has no semantic meaning (i.e. and are exactly equivalent), and while they were going to the trouble of doing that, they also specified that is illegal (the tag is always empty, so no need to close it), as is (arbitrary self-closing tags are not supported). Both of those misfeatures had been legal in XHTML, but approximately nobody had been using them, so it was reasonably safe to just yank them from the spec before they could turn into an attractive nuisance.

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Fedora and fallback DNS servers

Posted Feb 25, 2021 22:31 UTC (Thu) by pbonzini (subscriber, #60935) [Link] (2 responses)

Maybe not , but <td/> was certainly quite common in XHTML.

Fedora and fallback DNS servers

Posted Feb 26, 2021 0:42 UTC (Fri) by NYKevin (subscriber, #129325) [Link] (1 responses)

HTML5 solves that problem by specifying that you can just write <td> and then a closing tag is inferred at the next <td> or <th>, or at the end of the <tr>. This is not considered "error handling," either. It's perfectly legal to omit the closing tag, and the result is considered a well-formed HTML5 document. This was certainly never the case in XHTML, although I'm not sure how HTML4 handled this sort of chicanery.

If you do include the slash, it just strips it out and emits a parse error, so you would end up with an unclosed <td>. But as discussed in the previous paragraph, that <td> will probably close itself anyway, and so it hardly matters.

Incidentally, you can also do this with , meaning you can write prose like this:

Here is a paragraph of text...

Here is a second paragraph...

[and so on]

This is also considered well-formed HTML5.

Fedora and fallback DNS servers

Posted Feb 26, 2021 1:20 UTC (Fri) by jkingweb (subscriber, #113039) [Link]

> HTML5 solves that problem by specifying that you can just write <td> and then a closing tag is inferred at the next <td> or <th>, or at the end of the <tr>. This is not considered "error handling," either. It's perfectly legal to omit the closing tag, and the result is considered a well-formed HTML5 document. This was certainly never the case in XHTML, although I'm not sure how HTML4 handled this sort of chicanery.

This has been a design feature of HTML from its earliest days. Many end tags are optional, as are some start tags, including those for html, body, and tbody.

That last is perhaps lesser-known: in an HTML (but not XHTML) document, <tr> is never a child of <table>; there is always an implicit tbody (or explicit thead or tfoot) element in between.