def append_attribute(node, attribute, value)
      current_value = node.get_attribute(attribute) || ''
      current_values = current_value.split(/\s+/)
      updated_value = current_values | [value]
      node.set_attribute(attribute, updated_value.join(' '))
    end
def append_attribute(node, attribute, value)
      current_value = node.get_attribute(attribute) || ''
      current_values = current_value.split(/\s+/)
      updated_value = current_values | [value]
      node.set_attribute(attribute, updated_value.join(' '))
    end
If the attribute is not set, add it
 If the attribute is set, don't overwrite the existing value