def read_xml_value(xml_node):
  """Utility method for reading values from the plist XML.

  Args:
    xml_node: An ElementTree node, that contains a value.

  Returns:
    The value of the node, or None, if it could not be read.
  """
  if xml_node.tag == 'string':
    return xml_node.text
  elif xml_node.tag == 'integer':
    return int(xml_node.text)
  elif xml_node.tag == 'real':
    return float(xml_node.text)
  elif xml_node.tag == 'false':
    return 0
  elif xml_node.tag == 'true':
    return 1
  else:
    # other types of input are ignored.  (data, dates, arrays, etc.)
    return None