Register a callback for tag deletion.

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

def onTagDel(self, name, func):
        '''
        Register a callback for tag deletion.

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

        '''
        if '*' in name:
            self.ontagdelglobs.add(name, func)
        else:
            self.ontagdels[name].append(func)