Problems Trying to Pretty Print XSLT Output

this is my first post so please let me know if I can make it more constructive in any way. I have read the forum guidelines so if I inadvertantly break them in anyway it will be nothing more than an innocent mistake.

The Question

Is a simple one:

How do I pretty print the output of an XSL file?

But with some criteria:

Using only native XSL functionality.
Without having to use a second XSL file to do a 'second pass'.
It must also work for elements with mixed content.

I have googled this reasonably thoroughly but have not found a clear answer to this question. I have only used XSL for about a week so go easy if I have somehow missed the answer elsewhere.

An Example

This XML...

<email>
    <attachedItem>priceless photograph.jpg</attachedItem>
    <attachedItem>important document.doc</attachedItem>
    <attachedItem>access codes.pdf</attachedItem>
</email>

...Transformed by this XSL...

<!-- Pretty Print Output -->
<xsl:strip-space elements="*"/>
<xsl:output method="xml" indent="yes"/>

<xsl:template match="/">
<email>
    "Please find attached the stuff."
    <xsl:apply-templates/>
</email>
</xsl:template>

<xsl:template match="attachedItem">
    <xsl:copy/>
</xsl:template>

...Produces this result...

<?xml version="1.0" encoding="utf-8"?>
<email>
        "Please find attached the stuff."
        <attachedItem>priceless photograph.jpg</attachedItem>
   <attachedItem>important document.doc</attachedItem>
   <attachedItem>access codes.pdf</attachedItem>
</email>

Using the Saxon6.5.5 engine

Desired Output

<?xml version="1.0" encoding="utf-8"?>
<email>
   "Please find attached the stuff."
   <attachedItem>priceless photograph.jpg</attachedItem>
   <attachedItem>important document.doc</attachedItem>
   <attachedItem>access codes.pdf</attachedItem>
</email>

My Own Progress on the Problem

From the XSL above you will see I have discovered the use of <xsl:strip-space> and <xsl:output>. This meets the first 2 criteria but not the 3rd. In other words, it produces nice pretty printed XML without the mixed content, but with it I recieve the undesired output you can see above.

I know that the reason I get this output is because of the way whitespace is preserved in the source XML. White space is always preserved if it is part of a text node that contains other non-whitespace characters, regardless of the <xsl:strip-space> instructions. However despite my understanding I still cannot think of a solution.

Although I have addressed the first 2 criteria myself I would still like to know if this is the best way to achieve a pretty printed result.

Thanks in advance!

Solution

The following stylesheet produces exactly the output you request. The transformation was performed with Saxon 6.5.5. The correct indentation can only be achieved by meticulously typing all the line feed (
) and space ( )characters.

Note that pretty printing XML has no meaning when text content is concerned. The indentation of element tags can be easily controlled, but text nodes of elements with mixed content are always a problem. An application that takes XML as input should never rely on the exact indentation or whitespace handling of text content in XML.

In general, it is considered a bad idea to directly output literal text in an XSLT stylesheet. Always put text content inside xsl:text. xsl:strip-space has an effect only on whitespace-only text nodes of elements that belong to the input XML document (as suggested by @TobiasKlevenz already).

Stylesheet

<?xml version="1.0" encoding="UTF-8" ?>
<xsl:transform xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
    <!-- Pretty Print Output -->
<xsl:strip-space elements="*"/>
<xsl:output method="xml" indent="yes"/>

<xsl:template match="/">
<email>
    <xsl:text>&#10;&#32;&#32;&#32;"Please find attached the stuff."&#10;&#32;&#32;&#32;</xsl:text>
    <xsl:apply-templates/>
</email>
</xsl:template>

<xsl:template match="attachedItem|text()">
    <xsl:copy>
        <xsl:apply-templates/>
    </xsl:copy>
</xsl:template>

</xsl:transform>

Output

<?xml version="1.0" encoding="utf-8"?>
<email>
   "Please find attached the stuff."
   <attachedItem>priceless photograph.jpg</attachedItem>
   <attachedItem>important document.doc</attachedItem>
   <attachedItem>access codes.pdf</attachedItem>
</email>