4 ms·

The second and third examples do not have namespaces. How would you include an HTML summary, for example?

wtbob 10y ago
> The second and third examples do not have namespaces. > How would you include an HTML summary, for example? As a text attribute, honestly — which would be necessary in XML as well (you could embed XHTML in XML, but not HTML). And in the general case, embedding one variant of XML inside another, rather than embedding a character-encoded variant of XML inside another, doesn't seem all that useful. How often do transforms need to reach all the way in like that? I guess it's cool if it's possible, which is why I like S-expressions all the way down. But I don't think it's all that useful, as opposed to neat.
- erlehmann_ 10y ago
  > How often do transforms need to reach all the way in like that? In my experience, almost every time XSLT is used on real-world documents, those are documents with multiple namespaces. XSLT stylesheets themselves are also documents that have multiple namespaces. Example: Atom feeds often contain XHTML content. It is a common problem with RSS that it does not specify if the content of an element is HTML or plain text. I have found that arguments that doubt a feature is necassary from people who can not imagine use cases are almost invariably wrong, while arguments that doubt a feature is necessary from people who list use cases and why they think those are better solved otherwise or even left unsolved are often right. Your post seems like an example of the former; would you say that complex real-world content with namespaces could sway you in favor of them?
  - lmm 10y ago
    I would be convinced if I saw real-world examples where having namespaces gave an advantage over not having namespaces. I can see the value in specifying whether the content of a given node is XHTML or text. I can at least theoretically see value in allowing nesting XHTML without a layer of escaping. I can't see any non-theoretical way in which namespaces are necessary to accomplish these things.
    - erlehmann_ 10y ago
      Example: The XSLT stylesheet for this Atom feed generates a web page for each entry: http://news.dieweltistgarnichtso.net/notes/index.xml http://news.dieweltistgarnichtso.net/notes/index.xml In this setup, the Atom XML for each entry is generated from XHTML with XSLT, which makes it possible to automatically include an Atom enclosure element for every XHTML media element. To publish a podcast episode, it is enough to add a post with an <audio> or <video> element, as an XSLT stylesheet can “reach into” the XHTML content. Namespaces are also widely used in SVG, which uses the XLink specification for hyperlinks and can embed XHTML and MathML content. Since SVG can be embedded in (X)HTML, this means you can have an ATOM feed containing XHTML containing MathML and SVG that contains XHTML and all have it displayed correctly.
      - lmm 10y ago
        > Example: The XSLT stylesheet for this Atom feed generates a web page for each entry: http://news.dieweltistgarnichtso.net/notes/index.xml http://news.dieweltistgarnichtso.net/notes/index.xml > In this setup, the Atom XML for each entry is generated from XHTML with XSLT, which makes it possible to automatically include an Atom enclosure element for every XHTML media element. To publish a podcast episode, it is enough to add a post with an <audio> or <video> element. Sure. Why do you need namespaces to do that? Why couldn't you do it in XML-without-namespaces (or even JSON and some theoretical JSON-transformation-lanugage?) > Namespaces are also widely used in SVG, which uses the XLink specification for hyperlinks and can embed XHTML and MathML content. Again, why are namespaces necessary though? Why not just have a tag whose content is specified to be XHTML/MathML ? Wouldn't you want that anyway for the sake of human readability?
        erlehmann_ 10y ago
        XML without namespaces does not exist. If it existed, how would you differentiate between title and link elements in Atom and title and link elements in XHTML? They have the same element names, but do not have the same meaning and therefore must be processed differently. Namespaces ensure that any XML processor can know the language of each part of the input. Namespaces actually are the general mechanism with which you can specify that content is in another language: If you look at the feed source code, you can see that XHTML content is started with <div xmlns="http://www.w3.org/1999/xhtml"> http://www.w3.org/1999/xhtml"> and ends where that div element is closed. Having an element with the semantics that “this content is in another language” is done out of necessity in HTML, as it has no namespacing: <style> elements contain CSS, <script> elements contain JavaScript, <svg> elements contain SVG … having an element in each language to embed each other language would become complicated very fast.

wtbob 10y ago

> The second and third examples do not have namespaces. > How would you include an HTML summary, for example? As a text attribute, honestly — which would be necessary in XML as well (you could embed XHTML in XML, but not HTML). And in the general case, embedding one variant of XML inside another, rather than embedding a character-encoded variant of XML inside another, doesn't seem all that useful. How often do transforms need to reach all the way in like that? I guess it's cool if it's possible, which is why I like S-expressions all the way down. But I don't think it's all that useful, as opposed to neat.

erlehmann_ 10y ago
> How often do transforms need to reach all the way in like that? In my experience, almost every time XSLT is used on real-world documents, those are documents with multiple namespaces. XSLT stylesheets themselves are also documents that have multiple namespaces. Example: Atom feeds often contain XHTML content. It is a common problem with RSS that it does not specify if the content of an element is HTML or plain text. I have found that arguments that doubt a feature is necassary from people who can not imagine use cases are almost invariably wrong, while arguments that doubt a feature is necessary from people who list use cases and why they think those are better solved otherwise or even left unsolved are often right. Your post seems like an example of the former; would you say that complex real-world content with namespaces could sway you in favor of them?
- lmm 10y ago
  I would be convinced if I saw real-world examples where having namespaces gave an advantage over not having namespaces. I can see the value in specifying whether the content of a given node is XHTML or text. I can at least theoretically see value in allowing nesting XHTML without a layer of escaping. I can't see any non-theoretical way in which namespaces are necessary to accomplish these things.
  - erlehmann_ 10y ago
    Example: The XSLT stylesheet for this Atom feed generates a web page for each entry: http://news.dieweltistgarnichtso.net/notes/index.xml http://news.dieweltistgarnichtso.net/notes/index.xml In this setup, the Atom XML for each entry is generated from XHTML with XSLT, which makes it possible to automatically include an Atom enclosure element for every XHTML media element. To publish a podcast episode, it is enough to add a post with an <audio> or <video> element, as an XSLT stylesheet can “reach into” the XHTML content. Namespaces are also widely used in SVG, which uses the XLink specification for hyperlinks and can embed XHTML and MathML content. Since SVG can be embedded in (X)HTML, this means you can have an ATOM feed containing XHTML containing MathML and SVG that contains XHTML and all have it displayed correctly.
    - lmm 10y ago
      > Example: The XSLT stylesheet for this Atom feed generates a web page for each entry: http://news.dieweltistgarnichtso.net/notes/index.xml http://news.dieweltistgarnichtso.net/notes/index.xml > In this setup, the Atom XML for each entry is generated from XHTML with XSLT, which makes it possible to automatically include an Atom enclosure element for every XHTML media element. To publish a podcast episode, it is enough to add a post with an <audio> or <video> element. Sure. Why do you need namespaces to do that? Why couldn't you do it in XML-without-namespaces (or even JSON and some theoretical JSON-transformation-lanugage?) > Namespaces are also widely used in SVG, which uses the XLink specification for hyperlinks and can embed XHTML and MathML content. Again, why are namespaces necessary though? Why not just have a tag whose content is specified to be XHTML/MathML ? Wouldn't you want that anyway for the sake of human readability?
      - erlehmann_ 10y ago
        XML without namespaces does not exist. If it existed, how would you differentiate between title and link elements in Atom and title and link elements in XHTML? They have the same element names, but do not have the same meaning and therefore must be processed differently. Namespaces ensure that any XML processor can know the language of each part of the input. Namespaces actually are the general mechanism with which you can specify that content is in another language: If you look at the feed source code, you can see that XHTML content is started with <div xmlns="http://www.w3.org/1999/xhtml"> http://www.w3.org/1999/xhtml"> and ends where that div element is closed. Having an element with the semantics that “this content is in another language” is done out of necessity in HTML, as it has no namespacing: <style> elements contain CSS, <script> elements contain JavaScript, <svg> elements contain SVG … having an element in each language to embed each other language would become complicated very fast.