XSLT Match attribute and then its element - xslt

Question

In my source XML, any element can have an #n attribute. If one does, I want to output it before processing the element and all its children.
For example
<line n="2">Ipsum lorem</line>
<verse n="5">The sounds of silence</verse>
<verse>Four score and seven</verse>
<sentence n="3">
<word n="1">Hello</word>
<word n="2">world</word>
</sentence>
I have templates that match "line", "verse", "sentence" and "word". If any of those elements has an #n value, I want to output it in front of whatever the element's template generates.
The above might come out something like
2 <div class="line">Ipsum lorem</span>
5 <span class="verse">The sounds of silence</span>
<span class="verse">Four score and seven</span>
3 <p class="sentence">
1 <span class="word">Hello</span>
2 <span class="word">world</span>
</p>
where the templates for "line", "verse", etc. generated the div, span and p elements.
How should I think of this problem? -- Match the attribute and then apply-templates to its parent? (What would the syntax for that be?) Put a call-template at the beginning of every element's template? (That's unappealing.) Something else? (Probably!)
I tried a few things but got either an infinite loop, or nothing, or processing of the attribute and then its parent's children, but not the parent itself.

Answer 1

To simplify matters, I've placed the mapping from XML to HTML elements in an in-document data structure (accessible via the document() function with no arguments). Now only one template is needed requiring special processing of the #n attribute in only one place.
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="html"/>
<map>
<elt xml="line" html="class"/>
<elt xml="verse" html="span"/>
<elt xml="sentence" html="p"/>
<elt xml="word" html="span"/>
</map>
<xsl:template match="line|verse|sentence|word">
<xsl:if test="#n"><xsl:value-of select="#n"/> </xsl:if>
<xsl:element name="{document()/map/elt[#xml=name()]/#html}">
<xsl:attribute name="class"><xsl:value-of select="name()"/></xsl:attibute>
<xsl:apply-templates/>
</xsl:element>
</xsl:template>

Answer 2

Here is one simple way to do this:
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:strip-space elements="*"/>
<xsl:template match="*/*[#n]">
<xsl:value-of select="concat('
', #n, ' ')"/>
<xsl:apply-templates select="self::*" mode="content"/>
</xsl:template>
<xsl:template match="*/*[not(#*)]">
<xsl:apply-templates select="." mode="content"/>
</xsl:template>
<xsl:template match="line" mode="content">
<div class="line"><xsl:apply-templates/></div>
</xsl:template>
<xsl:template match="verse | word" mode="content">
<span class="{name()}"><xsl:apply-templates mode="content"/></span>
</xsl:template>
<xsl:template match="sentence" mode="content">
<p class="sentence"><xsl:apply-templates/></p>
</xsl:template>
</xsl:stylesheet>
when this transformation is applied on the provided XML document:
<t>
<line n="2">Ipsum lorem</line>
<verse n="5">The sounds of silence</verse>
<verse>Four score and seven</verse>
<sentence n="3">
<word n="1">Hello</word>
<word n="2">world</word>
</sentence>
</t>
the wanted, correct result is produced:
2 <div class="line">Ipsum lorem</div>
5 <span class="verse">The sounds of silence</span>
<span class="verse">Four score and seven</span>
3 <p class="sentence">
1 <span class="word">Hello</span>
2 <span class="word">world</span>
</p>
Explanation: Appropriate use of templates and modes.