The source code

    // We are adding these custom layouts to a namespace that does not
    // exist by default in Ext, so we have to add the namespace first:
    Ext.ns('Ext.ux.layout');

    /**
     * @class Ext.ux.layout.RowLayout
     * @extends Ext.layout.ContainerLayout
     * This is the layout style of choice for creating structural layouts in a multi-row format where the height of
     * each row can be specified as a percentage or fixed height.  Row widths can also be fixed, percentage or auto.
     * This class is intended to be extended or created via the layout:'ux.row' {@link Ext.Container#layout} config,
     * and should generally not need to be created directly via the new keyword.
     * RowLayout does not have any direct config options (other than inherited ones), but it does support a
     * specific config property of rowHeight that can be included in the config of any panel added to it.  The
     * layout will use the rowHeight (if present) or height of each panel during layout to determine how to size each panel.
     * If height or rowHeight is not specified for a given panel, its height will default to the panel's height (or auto).
     * The height property is always evaluated as pixels, and must be a number greater than or equal to 1.
     * The rowHeight property is always evaluated as a percentage, and must be a decimal value greater than 0 and
     * less than 1 (e.g., .25).
     * The basic rules for specifying row heights are pretty simple.  The logic makes two passes through the
     * set of contained panels.  During the first layout pass, all panels that either have a fixed height or none
     * specified (auto) are skipped, but their heights are subtracted from the overall container height.  During the second
     * pass, all panels with rowHeights are assigned pixel heights in proportion to their percentages based on
     * the total remaining container height.  In other words, percentage height panels are designed to fill the space
     * left over by all the fixed-height and/or auto-height panels.  Because of this, while you can specify any number of rows
     * with different percentages, the rowHeights must always add up to 1 (or 100%) when added together, otherwise your
     * layout may not render as expected.  Example usage:
     *
    // All rows are percentages -- they must add up to 1
    var p = new Ext.Panel({
        title: 'Row Layout - Percentage Only',
        layout:'ux.row',
        items: [{
            title: 'Row 1',
            rowHeight: .25
        },{
            title: 'Row 2',
            rowHeight: .6
        },{
            title: 'Row 3',
            rowHeight: .15
        }]
    });

    // Mix of height and rowHeight -- all rowHeight values must add
    // up to 1. The first row will take up exactly 120px, and the last two
    // rows will fill the remaining container height.
    var p = new Ext.Panel({
        title: 'Row Layout - Mixed',
        layout:'ux.row',
        items: [{
            title: 'Row 1',
            height: 120,
            // standard panel widths are still supported too:
            width: '50%' // or 200
        },{
            title: 'Row 2',
            rowHeight: .8,
            width: 300
        },{
            title: 'Row 3',
            rowHeight: .2
        }]
    });

     */
    Ext.ux.layout.RowLayout = Ext.extend(Ext.layout.ContainerLayout, {
        // private
        monitorResize:true,

        // private
        isValidParent : function(c, target){
            return c.getEl().dom.parentNode == this.innerCt.dom;
        },

        // private
        onLayout : function(ct, target){
            var rs = ct.items.items, len = rs.length, r, i;

            if(!this.innerCt){
                target.addClass('ux-row-layout-ct');
                this.innerCt = target.createChild({cls:'x-row-inner'});
            }
            this.renderAll(ct, this.innerCt);

            var size = target.getViewSize();

            if(size.width < 1 && size.height < 1){ // display none?
                return;
            }

            var h = size.height - target.getPadding('tb'),
                ph = h;

            this.innerCt.setSize({height:h});

            // some rows can be percentages while others are fixed
            // so we need to make 2 passes

            for(i = 0; i < len; i++){
                r = rs[i];
                if(!r.rowHeight){
                    ph -= (r.getSize().height + r.getEl().getMargins('tb'));
                }
            }

            ph = ph < 0 ? 0 : ph;

            for(i = 0; i < len; i++){
                r = rs[i];
                if(r.rowHeight){
                    r.setSize({height: Math.floor(r.rowHeight*ph) - r.getEl().getMargins('tb')});
                }
            }
        }

        /**
         * @property activeItem
         * @hide
         */
    });

    Ext.Container.LAYOUTS['ux.row'] = Ext.ux.layout.RowLayout;