The source code

    /**
     * @class Ext.grid.Column
     * This class encapsulates column configuration data to be used in the initialization of a
     * {@link Ext.grid.ColumnModel ColumnModel}.
     * While subclasses are provided to render data in different ways, this class renders a passed
     * data field unchanged and is usually used for textual columns.
     */
    Ext.grid.Column = function(config){
        Ext.apply(this, config);

        if(typeof this.renderer == 'string'){
            this.renderer = Ext.util.Format[this.renderer];
        } else if(Ext.isObject(this.renderer)){
            this.scope = this.renderer.scope;
            this.renderer = this.renderer.fn;
        }
        this.renderer = this.renderer.createDelegate(this.scope || config);

        if(this.id === undefined){
            this.id = ++Ext.grid.Column.AUTO_ID;
        }
        if(this.editor){
            this.editor = Ext.create(this.editor, 'textfield');
        }
    };

    Ext.grid.Column.AUTO_ID = 0;

    Ext.grid.Column.prototype = {
        /**
         * @cfg {Boolean} editable Optional. Defaults to true, enabling the configured
         * {@link #editor}.  Set to false to initially disable editing on this column.
         * The initial configuration may be dynamically altered using
         * {@link Ext.grid.ColumnModel}.{@link Ext.grid.ColumnModel#setEditable setEditable()}.
         */
        /**
         * @cfg {String} id Optional. A name which identifies this column (defaults to the column's initial
         * ordinal position.) The id is used to create a CSS class name which is applied to all
         * table cells (including headers) in that column (in this context the id does not need to be
         * unique). The class name takes the form of x-grid3-td-id
         * Header cells will also receive this class name, but will also have the class x-grid3-hd
         * So, to target header cells, use CSS selectors such as:.x-grid3-hd-row .x-grid3-td-id
         * The {@link Ext.grid.GridPanel#autoExpandColumn} grid config option references the column via this
         * unique identifier.
         */
        /**
         * @cfg {String} header Optional. The header text to be used as innerHTML
         * (html tags are accepted) to display in the Grid view.  Note: to
         * have a clickable header with no text displayed use ' '.
         */
        /**
         * @cfg {Boolean} groupable Optional. If the grid is being rendered by an {@link Ext.grid.GroupingView}, this option
         * may be used to disable the header menu item to group by the column selected. Defaults to true,
         * which enables the header menu group option.  Set to false to disable (but still show) the
         * group option in the header menu for the column. See also {@link #groupName}.
         */
        /**
         * @cfg {String} groupName Optional. If the grid is being rendered by an {@link Ext.grid.GroupingView}, this option
         * may be used to specify the text with which to prefix the group field value in the group header line.
         * See also {@link #groupRenderer} and
         * {@link Ext.grid.GroupingView}.{@link Ext.grid.GroupingView#showGroupName showGroupName}.
         */
        /**
         * @cfg {Function} groupRenderer Optional. If the grid is being rendered by an {@link Ext.grid.GroupingView}, this option
         * may be used to specify the function used to format the grouping field value for display in the group
         * {@link #groupName header}.  If a groupRenderer is not specified, the configured
         * {@link #renderer} will be called; if a {@link #renderer} is also not specified
         * the new value of the group field will be used.
         * The called function (either the groupRenderer or {@link #renderer}) will be
         * passed the following parameters:
         *
         * v : ObjectThe new value of the group field.
         * unused : undefinedUnused parameter.
         * r : Ext.data.RecordThe Record providing the data
         * for the row which caused group change.
         * rowIndex : NumberThe row index of the Record which caused group change.
         * colIndex : NumberThe column index of the group field.
         * ds : Ext.data.StoreThe Store which is providing the data Model.
         *
         * The function should return a string value.
         */
        /**
         * @cfg {String} emptyGroupText Optional. If the grid is being rendered by an {@link Ext.grid.GroupingView}, this option
         * may be used to specify the text to display when there is an empty group value. Defaults to the
         * {@link Ext.grid.GroupingView}.{@link Ext.grid.GroupingView#emptyGroupText emptyGroupText}.
         */
        /**
         * @cfg {String} dataIndex Required. The name of the field in the
         * grid's {@link Ext.data.Store}'s {@link Ext.data.Record} definition from
         * which to draw the column's value.
         */
        /**
         * @cfg {Number} width
         * Optional. The initial width in pixels of the column.
         * The width of each column can also be affected if any of the following are configured:
         *
         * {@link Ext.grid.GridPanel}.{@link Ext.grid.GridPanel#autoExpandColumn autoExpandColumn}
         * {@link Ext.grid.GridView}.{@link Ext.grid.GridView#forceFit forceFit}
         *
         * By specifying forceFit:true, {@link #fixed non-fixed width} columns will be
         * re-proportioned (based on the relative initial widths) to fill the width of the grid so
         * that no horizontal scrollbar is shown.
         *
         * {@link Ext.grid.GridView}.{@link Ext.grid.GridView#autoFill autoFill}
         * {@link Ext.grid.GridPanel}.{@link Ext.grid.GridPanel#minColumnWidth minColumnWidth}
         *
    Note: when the width of each column is determined, a space on the right side
         * is reserved for the vertical scrollbar.  The
         * {@link Ext.grid.GridView}.{@link Ext.grid.GridView#scrollOffset scrollOffset}
         * can be modified to reduce or eliminate the reserved offset.
         */
        /**
         * @cfg {Boolean} sortable Optional. true if sorting is to be allowed on this column.
         * Defaults to the value of the {@link #defaultSortable} property.
         * Whether local/remote sorting is used is specified in {@link Ext.data.Store#remoteSort}.
         */
        /**
         * @cfg {Boolean} fixed Optional. true if the column width cannot be changed.  Defaults to false.
         */
        /**
         * @cfg {Boolean} resizable Optional. false to disable column resizing. Defaults to true.
         */
        /**
         * @cfg {Boolean} menuDisabled Optional. true to disable the column menu. Defaults to false.
         */
        /**
         * @cfg {Boolean} hidden Optional. true to hide the column. Defaults to false.
         */
        /**
         * @cfg {String} tooltip Optional. A text string to use as the column header's tooltip.  If Quicktips
         * are enabled, this value will be used as the text of the quick tip, otherwise it will be set as the
         * header's HTML title attribute. Defaults to ''.
         */
        /**
         * @cfg {Mixed} renderer
         * For an alternative to specifying a renderer see {@link #xtype}
         * Optional. A renderer is an 'interceptor' method which can be used transform data (value,
         * appearance, etc.) before it is rendered). This may be specified in either of three ways:
         *
         * A renderer function used to return HTML markup for a cell given the cell's data value.
         * A string which references a property name of the {@link Ext.util.Format} class which
         * provides a renderer function.
         * An object specifying both the renderer function, and its execution scope (this
         * reference) e.g.:
    {
        fn: this.gridRenderer,
        scope: this
    }

         * If not specified, the default renderer uses the raw data value.
         * For information about the renderer function (passed parameters, etc.), see
         * {@link Ext.grid.ColumnModel#setRenderer}. An example of specifying renderer function inline:
    var companyColumn = {
       header: 'Company Name',
       dataIndex: 'company',
       renderer: function(value, metaData, record, rowIndex, colIndex, store) {
          // provide the logic depending on business rules
          // name of your own choosing to manipulate the cell depending upon
          // the data in the underlying Record object.
          if (value == 'whatever') {
              //metaData.css : String : A CSS class name to add to the TD element of the cell.
              //metaData.attr : String : An html attribute definition string to apply to
              //                         the data container element within the table
              //                         cell (e.g. 'style="color:red;"').
              metaData.css = 'name-of-css-class-you-will-define';
          }
          return value;
       }
    }
         *
         * See also {@link #scope}.
         */
        /**
         * @cfg {String} xtype Optional. A String which references a predefined {@link Ext.grid.Column} subclass
         * type which is preconfigured with an appropriate {@link #renderer} to be easily
         * configured into a ColumnModel. The predefined {@link Ext.grid.Column} subclass types are:
         *
         * gridcolumn : {@link Ext.grid.Column} (Default)
         * booleancolumn : {@link Ext.grid.BooleanColumn}
         * numbercolumn : {@link Ext.grid.NumberColumn}
         * datecolumn : {@link Ext.grid.DateColumn}
         * templatecolumn : {@link Ext.grid.TemplateColumn}
         *
         * Configuration properties for the specified xtype may be specified with
         * the Column configuration properties, for example:
         *
    var grid = new Ext.grid.GridPanel({
        ...
        columns: [{
            header: 'Last Updated',
            dataIndex: 'lastChange',
            width: 85,
            sortable: true,
            //renderer: Ext.util.Format.dateRenderer('m/d/Y'),
            xtype: 'datecolumn', // use xtype instead of renderer
            format: 'M/d/Y' // configuration property for {@link Ext.grid.DateColumn}
        }, {
            ...
        }]
    });
         *
         */
        /**
         * @cfg {Object} scope Optional. The scope (this reference) in which to execute the
         * renderer.  Defaults to the Column configuration object.
         */
        /**
         * @cfg {String} align Optional. Set the CSS text-align property of the column.  Defaults to undefined.
         */
        /**
         * @cfg {String} css Optional. An inline style definition string which is applied to all table cells in the column
         * (excluding headers). Defaults to undefined.
         */
        /**
         * @cfg {Boolean} hideable Optional. Specify as false to prevent the user from hiding this column
         * (defaults to true).  To disallow column hiding globally for all columns in the grid, use
         * {@link Ext.grid.GridPanel#enableColumnHide} instead.
         */
        /**
         * @cfg {Ext.form.Field} editor Optional. The {@link Ext.form.Field} to use when editing values in this column
         * if editing is supported by the grid. See {@link #editable} also.
         */

        // private. Used by ColumnModel to avoid reprocessing
        isColumn : true,
        /**
         * Optional. A function which returns displayable data when passed the following parameters:
         *
         * value : ObjectThe data value for the cell.
         * metadata : ObjectAn object in which you may set the following attributes:
         * css : StringA CSS class name to add to the cell's TD element.
         * attr : StringAn HTML attribute definition string to apply to the data container
         * element within the table cell (e.g. 'style="color:red;"').
         * record : Ext.data.recordThe {@link Ext.data.Record} from which the data was
         * extracted.
         * rowIndex : NumberRow index
         * colIndex : NumberColumn index
         * store : Ext.data.StoreThe {@link Ext.data.Store} object from which the Record
         * was extracted.
         *
         * @property renderer
         * @type Function
         */
        renderer : function(value){
            if(typeof value == 'string' && value.length < 1){
                return ' ';
            }
            return value;
        },

        // private
        getEditor: function(rowIndex){
            return this.editable !== false ? this.editor : null;
        },

        /**
         * Returns the {@link Ext.Editor editor} defined for this column that was created to wrap the {@link Ext.form.Field Field}
         * used to edit the cell.
         * @param {Number} rowIndex The row index
         * @return {Ext.Editor}
         */
        getCellEditor: function(rowIndex){
            var editor = this.getEditor(rowIndex);
            if(editor){
                if(!editor.startEdit){
                    if(!editor.gridEditor){
                        editor.gridEditor = new Ext.grid.GridEditor(editor);
                    }
                    return editor.gridEditor;
                }else if(editor.startEdit){
                    return editor;
                }
            }
            return null;
        }
    };

    /**
     * @class Ext.grid.BooleanColumn
     * @extends Ext.grid.Column
     * A Column definition class which renders boolean data fields.  See the {@link Ext.grid.ColumnModel#xtype xtype}
     * config option of {@link Ext.grid.ColumnModel} for more details.
     */
    Ext.grid.BooleanColumn = Ext.extend(Ext.grid.Column, {
        /**
         * @cfg {String} trueText
         * The string returned by the renderer when the column value is not falsey (defaults to 'true').
         */
        trueText: 'true',
        /**
         * @cfg {String} falseText
         * The string returned by the renderer when the column value is falsey (but not undefined) (defaults to
         * 'false').
         */
        falseText: 'false',
        /**
         * @cfg {String} undefinedText
         * The string returned by the renderer when the column value is undefined (defaults to ' ').
         */
        undefinedText: ' ',

        constructor: function(cfg){
            Ext.grid.BooleanColumn.superclass.constructor.call(this, cfg);
            var t = this.trueText, f = this.falseText, u = this.undefinedText;
            this.renderer = function(v){
                if(v === undefined){
                    return u;
                }
                if(!v || v === 'false'){
                    return f;
                }
                return t;
            };
        }
    });

    /**
     * @class Ext.grid.NumberColumn
     * @extends Ext.grid.Column
     * A Column definition class which renders a numeric data field according to a {@link #format} string.  See the
     * {@link Ext.grid.ColumnModel#xtype xtype} config option of {@link Ext.grid.ColumnModel} for more details.
     */
    Ext.grid.NumberColumn = Ext.extend(Ext.grid.Column, {
        /**
         * @cfg {String} format
         * A formatting string as used by {@link Ext.util.Format#number} to format a numeric value for this Column
         * (defaults to '0,000.00').
         */
        format : '0,000.00',
        constructor: function(cfg){
            Ext.grid.NumberColumn.superclass.constructor.call(this, cfg);
            this.renderer = Ext.util.Format.numberRenderer(this.format);
        }
    });

    /**
     * @class Ext.grid.DateColumn
     * @extends Ext.grid.Column
     * A Column definition class which renders a passed date according to the default locale, or a configured
     * {@link #format}. See the {@link Ext.grid.ColumnModel#xtype xtype} config option of {@link Ext.grid.ColumnModel}
     * for more details.
     */
    Ext.grid.DateColumn = Ext.extend(Ext.grid.Column, {
        /**
         * @cfg {String} format
         * A formatting string as used by {@link Date#format} to format a Date for this Column
         * (defaults to 'm/d/Y').
         */
        format : 'm/d/Y',
        constructor: function(cfg){
            Ext.grid.DateColumn.superclass.constructor.call(this, cfg);
            this.renderer = Ext.util.Format.dateRenderer(this.format);
        }
    });

    /**
     * @class Ext.grid.TemplateColumn
     * @extends Ext.grid.Column
     * A Column definition class which renders a value by processing a {@link Ext.data.Record Record}'s
     * {@link Ext.data.Record#data data} using a {@link #tpl configured} {@link Ext.XTemplate XTemplate}.
     * See the {@link Ext.grid.ColumnModel#xtype xtype} config option of {@link Ext.grid.ColumnModel} for more
     * details.
     */
    Ext.grid.TemplateColumn = Ext.extend(Ext.grid.Column, {
        /**
         * @cfg {String/XTemplate} tpl
         * An {@link Ext.XTemplate XTemplate}, or an XTemplate definition string to use to process a
         * {@link Ext.data.Record Record}'s {@link Ext.data.Record#data data} to produce a column's rendered value.
         */
        constructor: function(cfg){
            Ext.grid.TemplateColumn.superclass.constructor.call(this, cfg);
            var tpl = typeof Ext.isObject(this.tpl) ? this.tpl : new Ext.XTemplate(this.tpl);
            this.renderer = function(value, p, r){
                return tpl.apply(r.data);
            };
            this.tpl = tpl;
        }
    });

    /*
     * @property types
     * @type Object
     * @member Ext.grid.Column
     * @static
     * An object containing predefined Column classes keyed by a mnemonic code which may be referenced
     * by the {@link Ext.grid.ColumnModel#xtype xtype} config option of ColumnModel.
     * This contains the following properties
     * gridcolumn : {@link Ext.grid.Column Column constructor}
     * booleancolumn : {@link Ext.grid.BooleanColumn BooleanColumn constructor}
     * numbercolumn : {@link Ext.grid.NumberColumn NumberColumn constructor}
     * datecolumn : {@link Ext.grid.DateColumn DateColumn constructor}
     * templatecolumn : {@link Ext.grid.TemplateColumn TemplateColumn constructor}
     *
     */
    Ext.grid.Column.types = {
        gridcolumn : Ext.grid.Column,
        booleancolumn: Ext.grid.BooleanColumn,
        numbercolumn: Ext.grid.NumberColumn,
        datecolumn: Ext.grid.DateColumn,
        templatecolumn: Ext.grid.TemplateColumn
    };