How to use "<<" operator in XPATH 2.0?

Question

I am studying the concept of Node comparison in XPath 2.0. I am working with precedes operator << and getting an error below:

The value of attribute "select" associated with an element type "xsl: sequence" must not contain the '<' character.

I tried with XPath 2.0 precedes operator

<xsl:sequence select="/Root/*[../H1[2] << .]"/>

The below is the code I tried.

Input:

<?xml version="1.0" encoding="UTF-8"?>
<Root>
<H1>first</H1>
<p>Test</p>
<H1>second</H1>
<p/>
<p/>
<H1/>
<p/>
<p/>
</Root>

Processing: I am selecting the preceding element using << operator.

<?xml version="1.0" encoding="UTF-8"?>
    <xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="/">
    <xsl:sequence select="/Root/*[../H1[2] << .]"/>     
    </xsl:template>
    </xsl:stylesheet>

Issue:

The value of attribute "select" associated with an element type "xsl:sequence" must not contain the '<' character.

Expected result: To find the preceding element of H1[2] element by using << operator.

Answer 1

The XPath syntax is << but inside of an XML/XSLT document you need to escape it as <<.