Handles a keypress event on the picker element
@private
@param {Ext.EventObject} e
@param {HTMLElement} el
function(e, el) {
        var key = e.getKey();

        if(key === e.ENTER || (key === e.TAB && this.selectOnTab)) {
            this.selectItem(this.picker.getSelectionModel().getSelection()[0]);
        }
    }