5 ms·

Additionally, being conservative in what you accept forces people to be conservative in what they emit upstream. Win-win!

• unlinker 10y ago
  Tell that to HTML engines ;P
  • catnaroek 10y ago
    Has any browser implementor ever given it a serious try?
    • seba_dos1 10y ago
      XHTML?
      • catnaroek 10y ago
        That wasn't serious enough. Did any browser ever reject a Web page just because it wasn't well-formed XHTML? Basically, give people a hand, and they'll grab your whole arm. It's human nature, and Web developers aren't above it.
        • unlinker 10y ago
          That would be madness. Imagine a browser that did that, or that crashed the tab in case of a JS error. There would be no pages left :P
          • catnaroek 10y ago
            It would be a lot more sensible than you think. When I get a compilation error, what I do is take a breath, think about the meaning of my code, correct any logical mistakes I can find, and try to compile again. Why couldn't Web developers do the same? Also, there's no need to crash the tab. The browser could simply stop running any JavaScript, and leave the user with a static page.
            • Klathmon 10y ago
              IIRC some of the older versions of internet explorer did something like that, showing the user a popup if an error happened and asked them if they wanted to keep going.
              • catnaroek 10y ago
                Next, browsers will show users a popup asking if they want to jump off a cliff.
          • regularfry 10y ago
            And this is precisely the point. If the very earliest browsers had insisted on correctness rather than permissively accepting broken HTML (and JS - see semicolon insertion), we would not now have a situation where browsers need to do a ton of work to allow graceful degradation in the face of awful markup, simply because the tooling would have evolved in the other direction. Postel's Law gains a little temporary sender convenience in exchange for a nasty mess of permanent receiver headaches.
            • DanBC 10y ago
              Postel's law has two parts. Be gracious in what you receive is what most people are talking about, but be cautious in what you send is just as important. If people are using broken markup that's the problem that needs fixing. How many web devs bother with validation anymore? (And not for app like functionality, but for what should be simple text and images with a few menus - why are so many newspaper websites so awful?) https://tools.ietf.org/html/rfc793 https://tools.ietf.org/html/rfc793 2.10. Robustness Principle TCP implementations will follow a general principle of robustness: be conservative in what you do, be liberal in what you accept from others.
              • catnaroek 10y ago
                > but be cautious in what you send is just as important. How are you going to enforce this for everyone? > TCP implementations will follow a general principle of robustness (...) This rule has worked well for TCP implementors in large part because of their circumstances, which are very different from those of browser implementors and Web developers: (0) Priorities: How much do the following desiderata matter to each group: reliability, performance, new features? (1) Skill: What skills does a representative programmer from each group have? (2) Risk profile: How does each group cope with the possibility of design and implementation errors? How much technical debt are they willing to take? I'd contend that Postel's law doesn't scale beyond relatively small groups of highly skilled programmers, for whom reliability is paramount and trumps all other considerations.
              • regularfry 10y ago
                The problem is that being conservative and precise isn't enough. You and I can both be conservative, but disagree on the specifics (given an ambiguous spec, for instance). A permissive receiver of both our data now has to support both sides of our disagreement forever.
        • seba_dos1 10y ago
          >Did any browser ever reject a Web page just because it wasn't well-formed XHTML? Of course. If you served XHTML properly (by setting "application/xhtml+xml" MIME type), ill-formed XHTML would just show you a big syntax error instead of the page. Try it, that's still the case. Even when being well-formed, lots of sites still used "text/html" type to trigger HTML (SGML) parser instead of XML one, as any 3rd party code embedded into the website would of course crash the page as well. That was one of the reasons why XHTML never got popular and eventually has been abandoned.
          • catnaroek 10y ago
            That still wasn't serious enough. All it took to get browsers to accept non-XHTML pages was to change the MIME type. What I'm talking about is simply not displaying ill-formed pages at all, under any circumstances.
            • seba_dos1 10y ago
              But with that MIME type it wasn't XHTML at all. It was being parsed as HTML which was possible only because of big similarity between those two formats. All you need to ensure the behavior you want is to disable HTML parsing (which is pretty much ensures being liberal in what the parser accepts already in its specification).
      • alanh 10y ago
        Reply to sibling: “Did any browser reject poorly formed XHTML?” Yes, they did, if the XHTML was served with a MIME type of application/xhtml+xml. However, this MIME type was extremely rare because MSIE would not show a web page unless the MIME type was text/html. Furthermore, the extreme brittleness of XHTML was generally regarded as a Bad Move as one single URL in your source code with a literal ampersand instead of & would cause a complete and total breakage of your web page. Of course, many web pages are crummily concatenated strings and there are a lot of web devs who would never be able to reliably generate 100% XHTML-compliant output. Shit, pasting in a snippet of HTML where the BR tags omitted the self-closing slash would break your XHTML validation. tl;dr: Yes, and it sucked
        • catnaroek 10y ago
          See second reply to seba_dos1.