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What's the need for XHTML?

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佛祖请我去吃肉
佛祖请我去吃肉 2020-12-08 13:58

In an interview I was asked a question that I\'d never thought about, which was \"We already have HTML which fulfills all the requirements of writing a web page, so what\'s

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  • 攒了一身酷
    2020-12-08 14:24

    If i want to crawl your site, and parse its contents, i can only do it if it's XML.

    Parsing HTML is a nightmare.

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  • 滥情空心
    2020-12-08 14:25

    Because it is valid XML. That helps a lot since you can use a lot of tools originally designed for XML, such as XML parsers, XSLT, XPath, XQuery, ...

    Normal HTML is a SGML dialect and that is not parsable without knowledge of the schema.

    <ul>
    <li>one
    <li>two
    <li>three
</ul>

    is correct HTML but not correct XML. If you want to parse that, you have to know that ul-elements have to be closed but li s don't.

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  • 春和景丽
    2020-12-08 14:25

    I think that it helps browsers correctly display the html without making assumptions about where tags should be closed. Any time a browsers assumes something you know what happens.

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  • 刺人心
    2020-12-08 14:28

    Why was XHTML created?

    • HTML is not very extensible. XHTML aimed to fix this by introducing namespaces so that languages such as MathML or SVG could be included inline.
    • XMl is much simpler to parse than SGML (the format used by HTML before version 5)
    • Due to an overwhelming number of websites with errors, browsers attempted to correct incorrect markup. New browsers have had to attempt to correct it in the same way. XHTML tries to increase standards by specifying that only structurally correct code will display.

    How well has it succeeded?

    • XHTML is widely spread, but almost always served with the text/html MIME type due to incompatibilities with Internet Explorer (up to version 8). Many of these pages would actually break if served as XML. So none of the three advantages above have really materialised.
    • Many people chose to use XHTML as they thought it would provide better future compatibility. Work has stopped on XHTML2.0 and while HTML5 will have an XHTML serialisation, this seems to be receiving minimal attention. XHTML provides no future compatibility advantages for the forseeable future. Mozilla and Safari recommend using just HTML.
    • HTML with a strict DTD already has a much cleaner format. HTML5 will take this further by removing the transitional DTD, removing unnecessary elements and defining a standard way for parsing documents with a degree of backwards compatibility. Browsers will still correct errors for the HTML serialisation, rather than forcing the markup to be fixed, but at least they will do it in the same way. Those who care about correct code will use validators anyway.

    What is the need for XHTML?

    XHTML had laudable goals and maybe it will be able to deliver in the future. I can't recommend XHTML for the possible future advantages it might provide, when HTML is much easier now. You should only really use XHTML if previous code or your tools force you to.

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  • 面向向阳花
    2020-12-08 14:28

    In a nutshell: XHTML is often only beneficial and preferred over HTML whenever you want to use a XML based tool to manipulate/transform/generate HTML pages on the server side.

    Lot of examples can be found in component based MVC frameworks like Sun Oracle JSF which uses Facelets as a XHTML based view technology. The server side components are definied in XSD's and the pages are parsed using a SAX parser. You can even add a <!DOCTYPE html> to top of the page to let Facelets generate "pure" valid and strict HTML5. Microsoft ASP.NET MVC has a similar view technology.

    When you're hand-writing HTML, XHTML doesn't add much benefit, or it must be pushing off the "coolness" of using a (over)hyped technology.

    See also:

    • Should I start with HTML or XHTML
    • Is it possible to use JSF+Facelets with HTML 4/5?
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  • 情深已故
    2020-12-08 14:29

    XHTML is simply about communication between systems. HTML is very difficult to parse, because of the number of variations that can occur as to what is well formed. Since XML is strict in its interpretation, this problem has been removed.

    Think about a RESTful architecture. If a URL is permanent location to an item, then systems which would want to access this item should be able to consume the information returned from accessing the URL. XHTML doesn't make this possible per se, because a system could already parse the HTML and retrieve the necessary information. XML just makes this easier. There is no limiting predefined set of tags which make it difficult to classify data in a document (althought techinically you can do this in HTML, because browsers will ignore it). You can use whatever you want to classify what data is retrieved.

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