'Prototype method to generate the name for the URL query variable
for this widget, can be overwritten in subclasses.
@param resource: the resource
@return: the URL query variable name (or list of
variable names if there are multiple operators)'

def variable(self, resource, get_vars=None):

    opts = self.opts
    if ('selector' in opts):
        (label, selector) = (None, opts['selector'])
    else:
        (label, selector) = self._selector(resource, self.field)
    self.selector = selector
    if (not selector):
        return None
    if (self.alternatives and (get_vars is not None)):
        operator = self._operator(get_vars, selector)
        if operator:
            self.operator = operator
    if ('label' not in self.opts):
        self.opts['label'] = label
    return self._variable(selector, self.operator)
