You are using the library incorrectly. Take a look at the instructions here .
, , :
1) xsl:
<xsl:import href="string.xsl"/>
2) :
xmlns:str="http://xsltsl.org/string"
3) :
<xsl:template match="foo">
<xsl:call-template name="str:to-upper">
<xsl:with-param name="text">hello world</xsl:with-param>
</xsl:call-template>
</xsl:template>
HELLO WORLD.
UPDATE:
, . string.xsl, URL.