function snake_case(name, separator){
  separator = separator || '_';
  return name.replace(SNAKE_CASE_REGEXP, function(letter, pos) {
    return (pos ? separator : '') + letter.toLowerCase();
  });
}
@ngdoc function
@name angular.bootstrap
@description
Use this function to manually start up angular application.

See: {@link guide/dev_guide.bootstrap.manual_bootstrap Bootstrap}

@param {Element} element DOM element which is the root of angular application.
@param {Array<String|Function>=} modules an array of module declarations. See: {@link angular.module modules}
@returns {angular.module.auto.$injector} Returns the newly created injector for this app.