lib/Ext/mixin/Sortable.js
function(sorters, defaultDirection) {
        var currentSorters = this.getSorters();
        return this.insertSorters(currentSorters ? currentSorters.length : 0, sorters, defaultDirection);
    }
function(sorters, defaultDirection) {
        var currentSorters = this.getSorters();
        return this.insertSorters(currentSorters ? currentSorters.length : 0, sorters, defaultDirection);
    }
This method adds all the sorters in a passed array.
@param {Array} sorters An array with sorters. A sorter can be an instance of Ext.util.Sorter, a string
indicating a property name, an object representing an Ext.util.Sorter configuration,
or a sort function.
@param {String} defaultDirection The default direction for each sorter in the array. Defaults
to the value of {@link #defaultSortDirection}. Can be either 'ASC' or 'DESC'.