XSLT - Comparing preceding-sibling's elements with current's node element

Question

I have this XML file:

    
        Consorcio W3C
        

        

Answer 1

Almost correct.

<xsl:if test="preceding-sibling::recurso[1]/unidad != unidad">
</xsl:if>

The :: is for axes, not for moving along a path ("making a location step"). In XPath terminology:

preceding-sibling::recurso[1]/unidad != unidad
'''''''''''''''''  ++++++++++ ++++++
                          ###
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~

'  = axis name       (optional, defaults to "child")
+  = node test       (required)
#  = predicate       (optional, for filtering)
~  = location step   (required at least once per select expression)

The [1] is a shorthand for [position()=1].

The child axis is implicit in a location step, so this

preceding-sibling::recurso[1]/unidad != unidad

is equivalent to this:

preceding-sibling::recurso[1]/child::unidad != unidad