Processing

// The following short XML file called "mammals.xml" is parsed 
// in the code below. It must be in the project's "data" folder.
//
// <?xml version="1.0"?>
// <mammals>
//   <animal id="0" species="Capra hircus">Goat</animal>
//   <animal id="1" species="Panthera pardus">Leopard</animal>
//   <animal id="2" species="Equus zebra">Zebra</animal>
// </mammals>

XML xml;

void setup() {
  xml = loadXML("mammals.xml");
  XML firstChild = xml.getChild("animal");
  println(firstChild.getFloat("id"));
  firstChild.setFloat("id", 123.456789);
  println(firstChild.getFloat("id"));
}

// Sketch prints:
// 0.0
// 123.45679