Re: [xsl] Can a single XPath statement duplicate the functionality of this verbose <xsl:choose> statement?

[Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>]

Hi,

On 10/24/2011 7:33 PM, Michael Kay wrote:
> Note that in the XDM model used by XPath 2.0 and XSLT 2.0:
>
> (a) a document node can have multiple element children
>
> (b) any node (document nodes, element nodes, even text nodes) can be
> parentless, and thus be the root of a tree
>
> although neither of these conditions will arise in a tree that results
> from parsing well-formed XML.

The last point is important if you want to have an accounting for the 
muddle.

For various reasons including historical ones (SGML), XML documents are 
restricted to having a single element at the top level. This was and is 
often called the "root element".

Yet there may also be other constructs sitting next to it, such as 
comments and processing instructions, and since these too become nodes 
in the tree, it is useful to have a nominal root (a "document node" or 
"the root node" in XPath 1.0 parlance) to which they can all attach.

As Michael remarks, XDM (and indeed the XPath 1.0 model as well) does 
not impose the restriction that there can only be a single element child 
of a document node. It also does not require that every tree have a 
document node at the top.

So if you serialize, in XML syntax, a document with more than one 
element child of the document node, you will not get well-formed XML 
document, because it doesn't follow the rule "one element at the top". 
(This is the flip side of Mike's observation that you won't get a 
document with more than one element at the top from parsing an XML 
document.) You can, however, get a document fragment or "well-formed XML 
external parsed entity", which can be called into an XML document using 
an entity reference.

Cheers,
Wendell



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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
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