Re: XSLT 3.0: What is the correct "Deep Skip" template

We made a conscious decision that deep-skip should work differently for
document nodes, because it was found that otherwise, the effect of failing to
supply an explicit template rule for the document node was very bewildering. A
built-in template rule for document nodes that skips the whole document is
simply not useful; it has to be overridden.

The change was documented in item 27 of appendix K, though there is no link to
the rationale used.

Michael Kay
Saxonica
mike@xxxxxxxxxxxx
+44 (0) 118 946 5893




On 2 Jan 2015, at 21:07, Dimitre Novatchev <dnovatchev@xxxxxxxxx> wrote:

> Let me start with wishing to everyone a Happy and Safe New Year!
>
>
> To continue with more routine, daily stuff :
>
> In section "6.7.4 Built-in Templates: Deep Skip" of the 2nd Last Call
> of the W3C "XSLT 3.0" specification
>
(http://www.w3.org/TR/2014/WD-xslt-30-20141002/#built-in-templates-deep-skip)
,
> we read:
>
> 'The effect of processing a tree using a mode that specifies
> on-no-match="deep-skip" is that where no explicit template rule is
> specified for an element, that element and all its descendants are
> ignored, and are not copied to the result tree.
>
> The effect of choosing on-no-match="deep-skip" is as follows:
>
> The built-in rule for document nodes is equivalent to calling
> xsl:apply-templates with no select attribute, and with the mode
> attribute set to #current. If the built-in rule was invoked with
> parameters, those parameters are passed on in the implicit
> xsl:apply-templates instruction.
>
> In the case where there are no parameters, this is equivalent to the
> following rule:
>
> <xsl:template match="document-node()" mode="M">
>  <xsl:apply-templates mode="#current"/>
> </xsl:template>
>
> The built-in rule for all items other than document nodes (that is,
> for all other kinds of node, as well as atomic values and functions,
> including maps) is to do nothing, that is, to return an empty sequence
> (without applying templates to any children or ancestors).
>
> This is equivalent to the following rule:
>
> <xsl:template match="." mode="M"/> '
>
>
> This definition raises some questions:
>
> 1. Why should there be inside a "deep skip" template, an
> <xsl:apply-templates> instruction?  If the purpose is really "deep
> skip", isn't this most directly accomplished by:
>
>      <xsl:template match="document-node()" mode="M"/>
>
>    And why pass parameters, if they wouldn't be used at all?
>
> 2. Why are there two separate "deep skip" built-in templates -- one
> for matching document nodes and one for matching any item? Why not
> just have a single template that matches any item (document node
> included):
>
>     <xsl:template match="." mode="M"/>
>
>
>
> --
> Cheers,
> Dimitre Novatchev