ruby - Can I change the XML node content using the Nokogiri .content method?

Question

the goal of the code below is to take an XML code. Take out of it the tag vco:parameter, clone it Replace both name and value and insert it back into the XML text. However, when I'm trying to replace the content of a subnode:

  cloneParam.at( '//vco:string' ).content = param[ :value ]

I see that changes were done, when I retrive this subnode

  puts "Node values: #{cloneParam.at( '//vco:string' ).to_xml}"

But when I'm trying to convert the whole node back to XML I see that changes are cone and

<vco:string>value</vco:string> 

has the old value....

 puts "Parameter  : #{cloneParam.to_xml}"

What was done wrong here?

#
# Input
#   params = [ {name=>parameterName, value=>parametersValue} ... ] 
#   Currently only string parameters are supported
# Output
#   XML string supported by vCO
# 
def self.prepareWorkflowParameters( params )
    executionContext =  
        '<?xml version="1.0" encoding="Windows-1251"?>
        <vco:execution-context xmlns:vco="http://www.vmware.com/vco" xmlns="vco">
            <vco:parameters>
                <vco:parameter name="name" type="string" description="" scope="local">      
                    <vco:string>value</vco:string>
                </vco:parameter>
            </vco:parameters>
        </vco:execution-context>'



    docExCon = Nokogiri.XML(executionContext)
    docParam = docExCon.xpath( '//vco:parameter' ).first.clone
    puts "Parameter clone 1: #{docParam.to_xml}"
    docExCon.xpath('//vco:parameter' ).first.remove
    puts "Parameter clone 1 after deletion: #{docParam.to_xml}"

    params.each do | param | 

        puts "Parameter clone 1 before cloning: #{docParam.to_xml}"
        cloneParam = docParam.clone
        puts "Parameter clone 2: #{cloneParam.to_xml}"

        cloneParam[ 'name' ] = param[ :name ]
        puts "Parameter clone 2: #{cloneParam.to_xml}"
        cloneParam.at( '//vco:string' ).content = param[ :value ]

        puts "Node values: #{cloneParam.at( '//vco:string' ).to_xml}"
        puts "Parameter  : #{cloneParam.to_xml}"

        docExCon.xpath( '//vco:parameters' ).first.add_child( cloneParam )
        puts "docExCon    : #{docExCon.to_xml}"
    end
    return docExCon.to_xml
end