Extend attrbiute instead of setting it? - xslt

Question

I'm building a quite complex XSLT in order to generate some HTML markup.
On one my goal is to "extend" the class attribute of the generated markup using some templates.
Unfortunately, it does not works, because the XSLT tag <xsl:attribute> is only able to "set" attribute. Not to manipulate existing ones.
When I try, the original attribute is wiped.
Here is a small reproduction:
XML:
<node>
<item value="1" type="abc"/>
<item value="20" type="zxy"/>
</node>
XSL:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" encoding="utf-8" indent="no"/>
<xsl:template match="/">
<xsl:apply-templates />
</xsl:template>
<xsl:template match="/node/item">
<p class="{#type}">
<xsl:call-template name='rule1' />
<xsl:call-template name='rule2' />
</p>
</xsl:template>
<xsl:template name='rule1'>
<xsl:attribute name='class'>
<xsl:choose>
<xsl:when test="#value mod 2 = 0">alpha</xsl:when>
<xsl:otherwise>omega</xsl:otherwise>
</xsl:choose>
</xsl:attribute>
</xsl:template>
<xsl:template name='rule2'>
<xsl:attribute name='class'>
<xsl:choose>
<xsl:when test="#value mod 10 = 0">beta</xsl:when>
<xsl:otherwise>gamma</xsl:otherwise>
</xsl:choose>
</xsl:attribute>
</xsl:template>
</xsl:stylesheet>
I would like to output:
<?xml version="1.0" encoding="utf-8"?>
<p class="abc omega"/>
<p class="zxy beta alpha"/>
But it outputs
<?xml version="1.0" encoding="utf-8"?>
<p class="omega"/>
<p class="beta"/>
is it possible to preserve the original attribute, or retrieve it within the utility template to reuse it?

Answer 1

It would seem that this answer would only satisfy a single deep, non-reiterated-upon class.
Include this at the start of the template you are calling:
<xsl:variable name="type" select="#type"/>
And then when it comes to updating the attribute value, try:
<xsl:attribute select="class">
<xsl:choose>
<xsl:when test="#value mod 2 = 0">
<xsl:value-of select="concat($type, ' alpha')"/>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="concat($type, ' omega')"/>
</xsl:otherwise>
</xsl:choose>
</xsl:attribute>
Again, I'm not super comfortable with XSLT but I did just try something similar in a test recently and it worked a charm. Hope it helps.
EDIT: I'm not sure but you might have to put the escaped value for a "space" in the concat function, I forget.

Answer 2

An approaching solution could be (thanks to #aleski suggestions)
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" encoding="utf-8" indent="no"/>
<xsl:template match="/">
<xsl:apply-templates />
</xsl:template>
<xsl:template match="/node/item">
<p>
<xsl:attribute name='class'>
<xsl:value-of select="#type" />
<xsl:call-template name='rule1' />
<xsl:call-template name='rule2' />
</xsl:attribute>
</p>
</xsl:template>
<xsl:template name='rule1'>
<xsl:choose>
<xsl:when test="#value mod 2 = 0"><xsl:value-of select="' alpha'" /></xsl:when>
<xsl:otherwise><xsl:value-of select="' omega'" /></xsl:otherwise>
</xsl:choose>
</xsl:template>
<xsl:template name='rule2'>
<xsl:choose>
<xsl:when test="#value mod 10 = 0"><xsl:value-of select="' beta'" /></xsl:when>
<xsl:otherwise><xsl:value-of select="' gamma'" /></xsl:otherwise>
</xsl:choose>
</xsl:template>
</xsl:stylesheet>

Answer 3

Do you like obscure coding solutions? If so, you can re-write your solution as this:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" encoding="utf-8" indent="no"/>
<xsl:template match="/node/item">
<p class="{#type} {substring('alphaomega', 1 + 5 * (#value mod 2 = 0), 5)} {normalize-space(substring('beta gamma', 1 + 5 * (#value mod 10 = 0), 5))}">
</p>
</xsl:template>
</xsl:stylesheet>
So, have three Attribute Value Templates in one attribute. If you take a look at one of them...
{substring('alphaomega', 1 + 5 * (#value mod 10 = 0), 5)}
This takes advantage of the fact that "true" evaluates to 1 in a numeric expression, and "false" evaluates to 0. So, when the expression is true, the first five characters of the string are returned. When it is false, the next five characters are.