The source code

    // private
    // This is a support class used internally by the Grid components
    Ext.grid.GridEditor = function(field, config){
        Ext.grid.GridEditor.superclass.constructor.call(this, field, config);
        field.monitorTab = false;
    };

    Ext.extend(Ext.grid.GridEditor, Ext.Editor, {
        alignment: "tl-tl",
        autoSize: "width",
        hideEl : false,
        cls: "x-small-editor x-grid-editor",
        shim:false,
        shadow:false
    });