XInclude 1.1 (Last Call mark II)

Volume 17, Issue 11; 18 Dec 2014

Implementation experience, there's nothing like it.

Some time back, we got XInclude 1.1 wrapped up. It was all done but for the implementations.

XInclude 1.1, provides a few small extensions:

  • It allows non-XML fragment identifiers so that, for example, fragments of text/plain documents can be included.

  • It adds the ability to copy attributes into the included content; this allows authors to add annotations that allow a post-processing step to identify the XInclude boundaries. Identifying the boundaries allows such a step to perform other processing, such as ID/IDREF fixup.

  • Licenses implementations to provide support for additional fragment identifier schemes.

All well and good. The annotation mechanism was simple: any namespace qualified attributes on the xi:include element would be copied to the (top-level) included elementsThis is not a 100% solution, but it's well over 80%..

As ever, the struggle was between simplicity and expressive power. “Copy namespace qualified attributes” is simple. Its consequences: there's no way to annotate with attributes that aren't in a namespace and it copies the xml:* attributes, which has pros and cons. Pro: copying xml:id is definitely a “works for the simplest cases” duplicate ID fixup mechanism. Con: copying the xml:lang attribute is most likely to do the wrong thing.

And then there's xml:base. Implementation experience taught us that copying xml:base naïvely did the wrong thing. And doing the right thing was…complicated.

Live and learn.

So we're going back to Last Call (with a plan to go stright to PR once we have implementations). Here's what we changed.

  • We don't copy the xml:* attributes anymore. We still copy all other namespace qualified attributes.

  • There's a new XInclude attribute, set-xml-id (n.b. not in a namespace). The value specified is used as the value for the xml:id attribute on top-level included elements.

  • Forced to re-open the can of worms, we accepted the request to provide some mechanism to support annotations not in a namespace. Attributes in the “http://www.w3.org/2001/XInclude/local-attributes” namespace will be copied to attributes with no namespace.

    In other words, <xi:include xila:class="highlight" href="…"/> will annotate top-level elements with a class attribute (in no namespace, with the value “highlight”).

Share and enjoy. And implement, please.