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I think this is only true for HTML5, but previous versions of HTML supposedly weren't specced well enough to write a prefect parser. Fixing this was one of the

I think this is only true for HTML5, but previous versions of HTML supposedly weren't specced well enough to write a prefect parser. Fixing this was one of the goals of the HTML5 revision if I'm not mistaken.

lifthrasiir 6y ago
You are correct, but I don't think they are even slightly relevant in 2021.
bawolff 6y ago
Web browsers exist, therefore its possible to parse html, even earlier versions. You're right that the de jure spec did not match de facto html, and browsers didn't neccesarily agree with each other. But that's always true. GCC has language extensions that aren't part of the c spec, but you wouldn't say that c is impossible to parse. Old html may have taken it up to 11, but its not fair to say its impossible to parse.
- chrismorgan 6y ago
  Perl is famously unparseable: it’s impossible to determine a parse tree without executing the code. (HTML, however, was never unparseable, merely insufficiently defined.)
- uuidgen 6y ago
  No, not really. The browsers did guess a lot and did standard-deviating parsing because the typical uses were wrong and they had to work. Nobody would switch to a new browser that doesn't work with existing pages. Modern example - mXSS. Even though modern html have to be valid xml the browser will, instead of giving an error when served invalid html, transform what's given to make it standard-compliant.
  - bawolff 6y ago
    Modern html by definition is not valid XML, unless you are using the xml serialization of html5 which isn't really teccomended and nobody does. Really no version of the official html spec was valid xml other than XHTML which was never particularly popular. But i don't really see your point. An implementation having a different idea how to parse html than you think is correct is not the same thing as something being unparsable. Its a tautology that if there exists a computer progran to parse something than it is possible to parse it with a computer program.
anoncake 6y ago
Previous versions of HTML were based on SGML. You can write a perfect SGML parser, but the developers of web browsers couldn't be bothered.
- erik_seaberg 6y ago
  “Worse is better” strikes again. In the early days of markup hand written by amateurs, users preferred the browsers that tolerated mistakes. Now the language is defined by a common error handling procedure, instead of a grammar.

lifthrasiir 6y ago

You are correct, but I don't think they are even slightly relevant in 2021.

bawolff 6y ago

Web browsers exist, therefore its possible to parse html, even earlier versions. You're right that the de jure spec did not match de facto html, and browsers didn't neccesarily agree with each other. But that's always true. GCC has language extensions that aren't part of the c spec, but you wouldn't say that c is impossible to parse. Old html may have taken it up to 11, but its not fair to say its impossible to parse.

chrismorgan 6y ago
Perl is famously unparseable: it’s impossible to determine a parse tree without executing the code. (HTML, however, was never unparseable, merely insufficiently defined.)
uuidgen 6y ago
No, not really. The browsers did guess a lot and did standard-deviating parsing because the typical uses were wrong and they had to work. Nobody would switch to a new browser that doesn't work with existing pages. Modern example - mXSS. Even though modern html have to be valid xml the browser will, instead of giving an error when served invalid html, transform what's given to make it standard-compliant.
- bawolff 6y ago
  Modern html by definition is not valid XML, unless you are using the xml serialization of html5 which isn't really teccomended and nobody does. Really no version of the official html spec was valid xml other than XHTML which was never particularly popular. But i don't really see your point. An implementation having a different idea how to parse html than you think is correct is not the same thing as something being unparsable. Its a tautology that if there exists a computer progran to parse something than it is possible to parse it with a computer program.

anoncake 6y ago

Previous versions of HTML were based on SGML. You can write a perfect SGML parser, but the developers of web browsers couldn't be bothered.

erik_seaberg 6y ago
“Worse is better” strikes again. In the early days of markup hand written by amateurs, users preferred the browsers that tolerated mistakes. Now the language is defined by a common error handling procedure, instead of a grammar.