code: function addCallback(name, fn) {
      if (typeof fn !== 'function') throw 'error while trying to add a custom callback: argument must be a function';
      if (callbacks[name]) throw 'error while trying to add a custom callback: ' + name + ' already exists';
      callbacks[name] = fn;
  }
docs: Adds functional parameters, to be referenced at html data attributes.
  @memberof! vivalid.htmlInterface
  @function
  @example vivalid.htmlInterface.addCallback('onValidationFailure', function(invalid,pending,valid){ alert('input group is invalid!: '+invalid+ ' invalid, ' +pending+' pending, and ' +valid+' valid ' ); });
  @param {string} name
  @param {function} fn