How to modify XML w/o DOMDocument / SimpleXML / libxml?

<?xml version="1.0" encoding="ISO-8859-15"?>

<!DOCTYPE Finvoice SYSTEM "Finvoice.dtd">

<Finvoice Version="1.2">

  <BuyerPartyDetails>

    <BuyerOrganisationName>Example Name</BuyerOrganisationName>

    <BuyerPostalAddressDetails>

      <BuyerStreetName>Street Name</BuyerStreetName>

      <BuyerTownName>Town Name</BuyerTownName>

      <CountryCode>FI</CountryCode>

      <CountryName>Finland</CountryName>

    </BuyerPostalAddressDetails>

  </BuyerPartyDetails>

  <InvoiceDetails>

    <InvoiceDate Format="CCYYMMDD">20120130</InvoiceDate>

  </InvoiceDetails>

</Finvoice>

I need to make a script to update this kind of XML file with either PHP or Javascript. I made something with PHP DOMXPath , but it turned out that it's not an option - the server doesnt have the support for it.

All of these elements that are shown above in the xml, are supposed to be picked if needed to update/change the value in them.