Re: [xsl] The output of evaluating an XSLT transform is the same regardless of the order in which output elements are evaluated. Right?

["G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>]

At 2010-04-12 13:37 -0400, Costello, Roger L. wrote:
> Is this statement true or false:
>
>   XSLT elements that produce output can be
>   evaluated in any order.

"elements that produce output" is ambiguous.  There are literal 
result elements and there are instruction elements.  Both can be 
building the output.  I think your statement needs to focus not on 
the elements but on the stylesheet as a whole.

An entire stylesheet can be processed internally in any way so long 
as the end result is predictable where the specification prescribes 
it.  An instruction may despatch a number of nodes for processing and 
the end results are assembled in despatching order not completion 
order.  But within the processing of one of those despatched nodes, 
there may be the despatching of other nodes, and those nested ones 
need to be assembled in that despatched order before the end result 
is assembled in the order the set was despatched.

This is consistent with the nested nature of XML and the processing of XML.

And even my use of "despatching" implies that the processor is 
visiting the stylesheet nodes in order.  It only has to act as if it 
had visited the nodes in the stylesheet in order.

> Example: This XSLT produces two outputs:
>
>    <xsl:text>Hello</xsl:text>
>    <xsl:text>World</xsl:text>
>
> Is this statement true or false:
>
>    The output will always be "HelloWorld" regardless
>    of which <xsl:text> element is evaluated first.

True.

> Is this explanation correct:
>
> Explanation: the outputs produced by each XSLT element is placed in 
> an in-memory "result tree." Their position in the result tree 
> depends on the sequential order of the outputs in the XSLT document. 
> Thus, this XSLT element:
>
>    <xsl:text>World</xsl:text>
>
> occurs later in the XSLT document and so therefore it is placed 
> later in the result tree.

"later in the document?"  No ... it is encountered after the earlier 
one is encountered.  The order of template rules is arbitrary in XSLT 
so location in the XSLT document is not useful to your answer.  Consider:

  <xsl:call-template name="do-hello"/>
  <xsl:call-template name="do-world"/>
  ...
  <xsl:template name="do-world">
    <xsl:text>World</xsl:text>
  ...
  <xsl:template name="do-hello">
    <xsl:text>Hello</xsl:text>

The order of the two <xsl:text> instructions isn't helpful.  The 
order in which they are encountered is significant.  That is the 
"despatch order" I'm referring to.

> After the XSLT transform completes executing then the result tree is 
> serialized to an output file,

How the processor does it is irrelevant.  One processor may do it 
that way.  All processors do it as if it were done that way.  But the 
use of "in-memory" and "result tree" constructs or whatever is up to 
the processor.

> in document order,

"in the order despatched for processing" (which might not be document order).

> which result in "Hello" first and "World" second.

Always for your example, for all processors, but regardless of the innards.

How is the answer to this important to your work with XML and 
XSLT?  The innards of the processor don't impact on the end result.

I hope this helps.

. . . . . . . . . . Ken

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