Sets the text of the raw element (or creates the layer if does not exist)
        @param text: text of the raw layer
        @type text: string

def set_raw(self,text):
        """
        Sets the text of the raw element (or creates the layer if does not exist)
        @param text: text of the raw layer
        @type text: string
        """
        node_raw = self.root.find('raw')
        if node_raw is None:
            node_raw = etree.Element('raw')
            self.root.insert(0,node_raw)
        node_raw.text = etree.CDATA(text)