Re: [xsl] Comment nodes in XSLT files.

[Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>]

Hi Greg,

At 12:08 PM 4/12/2004, you wrote:
> Traditionally comments in Interpreted language files slows things down.  It
> there any practical experience with the impact of comment nodes in the XSLT
> files, or best practice guidance?

If you are referring to XML comments that appear in your stylesheets, as in

<xsl:template match="foo">
  <!-- my comment here explains what the heck is going on -->
  <xsl:apply-templates/>
</xsl:template>

I'd be seriously surprised to see them have much impact, if any at all, in 
performance.

XSLT tells me that comments in this tree are ignored: "the stylesheet is 
treated as if neither processing instruction nodes nor comment nodes were 
included in the tree that represents the stylesheet" [XSLT 3]. (In this 
they are unlike comments in the XML source document, which I can get by 
using the comment() node test). So the processor doesn't even see them. So 
your question reduces to whether the comments will slow parsing down and 
whether this might have any effect on time to process. The answer to this 
is no, not hardly.

In this, XSLT is unlike interpreted languages: not only is XSLT usually 
(always?) compiled before execution, but also it is compiled from a parsed 
tree, not from the XML source from which that tree is derived.

> I would like to find the balance point between too much and too little.

I'd urge you to stress maintainability over performance for this. Since the 
analogy to interpreted languages is misplaced, there's no reason to assume 
there's a performance problem unless you have positive evidence that it 
might be.

> We have also considered an XSLT comment scrubber between the saved source
> and the published source.  It would be easy to build, but if the runtime
> impact of leaving the comments in place is sufficiently small why introduce
> all the other headaches?
>
> I think the answer varies from one XSLT processor to another.  My particular
> interest is in .NET ( don't flame me please) but I have an interest in other
> processors as well.

Processors will vary, but no conformant processor will do anything with 
comments in the stylesheet.

Cheers,
Wendell


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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
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