'Extract the new config settings from the form and
update the config dict
@param config: the config dict
@param form: the configuration form
@return: the updated config dict (can be a replacement)
NB config must remain JSON-serializable'

def accept_config(self, config, form):

    formvars = form.vars
    xml = formvars.get('xml')
    if (xml is not None):
        config['xml'] = xml
    return config
