Is it invalid HTML to write “&” by itself? Why? [duplicate]

Question

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Do I really need to encode '&' as ' &' ?

I know that W3C recommends to "use "&" (ASCII decimal 38) instead of "&" to avoid confusion with the beginning of a character reference", and that tidy warns of an "unescaped & which should be written as &" but, these warnings not withstanding, is it valid to write (say) "Tiffany & Co." instead of the more cautios "Tiffany & Co."?

I know the example above renders as expected (i.e., the same) in all browsers I've tried, but this is a syntax question for the language lawyers out there. It looks to me that, as long as the expression is not of the form " &blah; ", it should be legitimate. (Same with using angle brackets if you don't write " <blah> ".)

As an aside, the fact that skipping </li>'s is not deemed a warning, while unescaped &'s are, speaks volumes of the inconsistency of HTML syntax. In fact, if we're going to rely on the parser's smarts, leaving out a </ul> (for instance) should be OK if the (unfinished) list is the very last part of the document: no </ul>, no </body>, no </html>... no possible ambiguity, right?

PS: I just found out that (sensible) unescaped angle brackets yield no warnings in tidy, but are detected as errors by W3C's validator, while unescaped ampersands give warnings in both places. Go figure...

Answer 1

Invalid? Yes. A free ampersand inside HTML markup will result in a parser error.

Can modern browsers ignore the error and parse correctly? Most likely.

But it is malformed HTML.