This is the head of the XML file I am using
<?xml version="1.0" encoding="UTF-8"?>
<sbml xmlns="http://www.sbml.org/sbml/level3/version1/core" level="3" version="1">
<model metaid="metaid0" id="bind2_sbml">
<listOfUnitDefinitions>
<unitDefinition id="second_order_rate">
<listOfUnits>
<unit scale="0" kind="litre" multiplier="1" exponent="1" />
<unit scale="-6" kind="mole" multiplier="1" exponent="-1" />
<unit scale="0" kind="second" multiplier="1" exponent="-1" />
</listOfUnits>
I tried using /sbml[@xmlns="http://www.sbml.org/sbml/level3/version1/core"]/model
as suggested by https://xmltoolbox.appspot.com/xpath_generator.html. But this doesn't work as can be checked using https://codebeautify.org/Xpath-Tester