Register a callback for tag addition.

        Args:
            name (str): The name of the tag or tag glob.
            func (function): The callback func(node, tagname, tagval).

def onTagAdd(self, name, func):
        '''
        Register a callback for tag addition.

        Args:
            name (str): The name of the tag or tag glob.
            func (function): The callback func(node, tagname, tagval).

        '''
        # TODO allow name wild cards
        if '*' in name:
            self.ontagaddglobs.add(name, func)
        else:
            self.ontagadds[name].append(func)