You're not alone in finding this confusing. Some highly experienced
people have given you incorrect information on this thread.
<!-- Function to fetch value of a key-string pair in plist -->
<xsl:function name="me:metadata">
<xsl:param name="label"/>
<xsl:value-of select="normalize-space($metadata/plist/dict/key[text()=$label]/following::node()[1]/text())"/>
</xsl:function>
This function is NOT returning a string, and it is NOT returning a document node as some have suggested. It is returning a text node, because that is what<xsl:value-of> creates. Unlike xsl:variable, xsl:function does not wrap the text node in a document node; in the absence of an "as" attribute on xsl:function, it returns the text node unchanged.
Although I always recommend using an "as" attribute on xsl:function and xsl:param to make it clear what the inputs and output to the function are expected to be, the simplest fix to this function is to change<xsl:value-of> to<xsl:sequence>. It's a common mistake to use xsl:value-of when there is no intention or need to create a text node. The normal default way of returning a result from a function should be to use xsl:sequence.
>Any idea why the test evaluates to true?
The effective boolean value of a node is always true. In fact, Saxon can
work out that this function will always return a text node, and it will
probably therefore decide that the EBV of the function call is true
without even calling the function.
Michael Kay
Saxonica