The source code

    /*!
     * Ext JS Library 3.2.1
     * Copyright(c) 2006-2010 Ext JS, Inc.
     * licensing@extjs.com
     * http://www.extjs.com/license
     */
    /**
     * @class Ext.layout.FormLayout
     * @extends Ext.layout.AnchorLayout
     * This layout manager is specifically designed for rendering and managing child Components of
     * {@link Ext.form.FormPanel forms}. It is responsible for rendering the labels of
     * {@link Ext.form.Field Field}s.
     *
     * This layout manager is used when a Container is configured with the layout:'form'
     * {@link Ext.Container#layout layout} config option, and should generally not need to be created directly
     * via the new keyword. See {@link Ext.Container#layout} for additional details.
     *
     * In an application, it will usually be preferrable to use a {@link Ext.form.FormPanel FormPanel}
     * (which is configured with FormLayout as its layout class by default) since it also provides built-in
     * functionality for {@link Ext.form.BasicForm#doAction loading, validating and submitting} the form.
     *
     * A {@link Ext.Container Container} using the FormLayout layout manager (e.g.
     * {@link Ext.form.FormPanel} or specifying layout:'form') can also accept the following
     * layout-specific config properties:
     * {@link Ext.form.FormPanel#hideLabels hideLabels}
     * {@link Ext.form.FormPanel#labelAlign labelAlign}
     * {@link Ext.form.FormPanel#labelPad labelPad}
     * {@link Ext.form.FormPanel#labelSeparator labelSeparator}
     * {@link Ext.form.FormPanel#labelWidth labelWidth}
     *
     *
     * Any Component (including Fields) managed by FormLayout accepts the following as a config option:
     *
     * {@link Ext.Component#anchor anchor}
     *
     *
     * Any Component managed by FormLayout may be rendered as a form field (with an associated label) by
     * configuring it with a non-null {@link Ext.Component#fieldLabel fieldLabel}. Components configured
     * in this way may be configured with the following options which affect the way the FormLayout renders them:
     *
     * {@link Ext.Component#clearCls clearCls}
     * {@link Ext.Component#fieldLabel fieldLabel}
     * {@link Ext.Component#hideLabel hideLabel}
     * {@link Ext.Component#itemCls itemCls}
     * {@link Ext.Component#labelSeparator labelSeparator}
     * {@link Ext.Component#labelStyle labelStyle}
     *
     *
     * Example usage:
     *
    // Required if showing validation messages
    Ext.QuickTips.init();

    // While you can create a basic Panel with layout:'form', practically
    // you should usually use a FormPanel to also get its form functionality
    // since it already creates a FormLayout internally.
    var form = new Ext.form.FormPanel({
        title: 'Form Layout',
        bodyStyle: 'padding:15px',
        width: 350,
        defaultType: 'textfield',
        defaults: {
            // applied to each contained item
            width: 230,
            msgTarget: 'side'
        },
        items: [{
                fieldLabel: 'First Name',
                name: 'first',
                allowBlank: false,
                {@link Ext.Component#labelSeparator labelSeparator}: ':' // override labelSeparator layout config
            },{
                fieldLabel: 'Last Name',
                name: 'last'
            },{
                fieldLabel: 'Email',
                name: 'email',
                vtype:'email'
            }, {
                xtype: 'textarea',
                hideLabel: true,     // override hideLabels layout config
                name: 'msg',
                anchor: '100% -53'
            }
        ],
        buttons: [
            {text: 'Save'},
            {text: 'Cancel'}
        ],
        layoutConfig: {
            {@link #labelSeparator}: '~' // superseded by assignment below
        },
        // config options applicable to container when layout='form':
        hideLabels: false,
        labelAlign: 'left',   // or 'right' or 'top'
        {@link Ext.form.FormPanel#labelSeparator labelSeparator}: '>>', // takes precedence over layoutConfig value
        labelWidth: 65,       // defaults to 100
        labelPad: 8           // defaults to 5, must specify labelWidth to be honored
    });

     */
    Ext.layout.FormLayout = Ext.extend(Ext.layout.AnchorLayout, {

        /**
         * @cfg {String} labelSeparator
         * See {@link Ext.form.FormPanel}.{@link Ext.form.FormPanel#labelSeparator labelSeparator}.  Configuration
         * of this property at the container level takes precedence.
         */
        labelSeparator : ':',

        /**
         * Read only. The CSS style specification string added to field labels in this layout if not
         * otherwise {@link Ext.Component#labelStyle specified by each contained field}.
         * @type String
         * @property labelStyle
         */

        /**
         * @cfg {Boolean} trackLabels
         * True to show/hide the field label when the field is hidden. Defaults to false.
         */
        trackLabels: false,

        type: 'form',

        onRemove: function(c){
            Ext.layout.FormLayout.superclass.onRemove.call(this, c);
            if(this.trackLabels){
                c.un('show', this.onFieldShow, this);
                c.un('hide', this.onFieldHide, this);
            }
            // check for itemCt, since we may be removing a fieldset or something similar
            var el = c.getPositionEl(),
                ct = c.getItemCt && c.getItemCt();
            if (c.rendered && ct) {
                if (el && el.dom) {
                    el.insertAfter(ct);
                }
                Ext.destroy(ct);
                Ext.destroyMembers(c, 'label', 'itemCt');
                if (c.customItemCt) {
                    Ext.destroyMembers(c, 'getItemCt', 'customItemCt');
                }
            }
        },

        // private
        setContainer : function(ct){
            Ext.layout.FormLayout.superclass.setContainer.call(this, ct);
            if(ct.labelAlign){
                ct.addClass('x-form-label-'+ct.labelAlign);
            }

            if(ct.hideLabels){
                Ext.apply(this, {
                    labelStyle: 'display:none',
                    elementStyle: 'padding-left:0;',
                    labelAdjust: 0
                });
            }else{
                this.labelSeparator = ct.labelSeparator || this.labelSeparator;
                ct.labelWidth = ct.labelWidth || 100;
                if(Ext.isNumber(ct.labelWidth)){
                    var pad = Ext.isNumber(ct.labelPad) ? ct.labelPad : 5;
                    Ext.apply(this, {
                        labelAdjust: ct.labelWidth + pad,
                        labelStyle: 'width:' + ct.labelWidth + 'px;',
                        elementStyle: 'padding-left:' + (ct.labelWidth + pad) + 'px'
                    });
                }
                if(ct.labelAlign == 'top'){
                    Ext.apply(this, {
                        labelStyle: 'width:auto;',
                        labelAdjust: 0,
                        elementStyle: 'padding-left:0;'
                    });
                }
            }
        },

        // private
        isHide: function(c){
            return c.hideLabel || this.container.hideLabels;
        },

        onFieldShow: function(c){
            c.getItemCt().removeClass('x-hide-' + c.hideMode);

            // Composite fields will need to layout after the container is made visible
            if (c.isComposite) {
                c.doLayout();
            }
        },

        onFieldHide: function(c){
            c.getItemCt().addClass('x-hide-' + c.hideMode);
        },

        //private
        getLabelStyle: function(s){
            var ls = '', items = [this.labelStyle, s];
            for (var i = 0, len = items.length; i < len; ++i){
                if (items[i]){
                    ls += items[i];
                    if (ls.substr(-1, 1) != ';'){
                        ls += ';';
                    }
                }
            }
            return ls;
        },

        /**
         * @cfg {Ext.Template} fieldTpl
         * A {@link Ext.Template#compile compile}d {@link Ext.Template} for rendering
         * the fully wrapped, labeled and styled form Field. Defaults to:
    new Ext.Template(
        '<div class="x-form-item {itemCls}" tabIndex="-1">',
            '<label for="{id}" style="{labelStyle}" class="x-form-item-label">{label}{labelSeparator}</label>',
            '<div class="x-form-element" id="x-form-el-{id}" style="{elementStyle}">',
            '</div><div class="{clearCls}"></div>',
        '</div>'
    );

         * This may be specified to produce a different DOM structure when rendering form Fields.
         * A description of the properties within the template follows:
         * itemCls : StringThe CSS class applied to the outermost div wrapper
         * that contains this field label and field element (the default class is 'x-form-item' and itemCls
         * will be added to that). If supplied, itemCls at the field level will override the default itemCls
         * supplied at the container level.
         * id : StringThe id of the Field
         * {@link #labelStyle} : String
         * A CSS style specification string to add to the field label for this field (defaults to '' or the
         * {@link #labelStyle layout's value for labelStyle}).
         * label : StringThe text to display as the label for this
         * field (defaults to '')
         * {@link #labelSeparator} : StringThe separator to display after
         * the text of the label for this field (defaults to a colon ':' or the
         * {@link #labelSeparator layout's value for labelSeparator}). To hide the separator use empty string ''.
         * elementStyle : StringThe styles text for the input element's wrapper.
         * clearCls : StringThe CSS class to apply to the special clearing div
         * rendered directly after each form field wrapper (defaults to 'x-form-clear-left')
         *
         * Also see {@link #getTemplateArgs}
         */

        /**
         * @private
         *
         */
        renderItem : function(c, position, target){
            if(c && (c.isFormField || c.fieldLabel) && c.inputType != 'hidden'){
                var args = this.getTemplateArgs(c);
                if(Ext.isNumber(position)){
                    position = target.dom.childNodes[position] || null;
                }
                if(position){
                    c.itemCt = this.fieldTpl.insertBefore(position, args, true);
                }else{
                    c.itemCt = this.fieldTpl.append(target, args, true);
                }
                if(!c.getItemCt){
                    // Non form fields don't have getItemCt, apply it here
                    // This will get cleaned up in onRemove
                    Ext.apply(c, {
                        getItemCt: function(){
                            return c.itemCt;
                        },
                        customItemCt: true
                    });
                }
                c.label = c.getItemCt().child('label.x-form-item-label');
                if(!c.rendered){
                    c.render('x-form-el-' + c.id);
                }else if(!this.isValidParent(c, target)){
                    Ext.fly('x-form-el-' + c.id).appendChild(c.getPositionEl());
                }
                if(this.trackLabels){
                    if(c.hidden){
                        this.onFieldHide(c);
                    }
                    c.on({
                        scope: this,
                        show: this.onFieldShow,
                        hide: this.onFieldHide
                    });
                }
                this.configureItem(c);
            }else {
                Ext.layout.FormLayout.superclass.renderItem.apply(this, arguments);
            }
        },

        /**
         * Provides template arguments for rendering the fully wrapped, labeled and styled form Field.
         * This method returns an object hash containing properties used by the layout's {@link #fieldTpl}
         * to create a correctly wrapped, labeled and styled form Field. This may be overriden to
         * create custom layouts. The properties which must be returned are:
         * itemCls : StringThe CSS class applied to the outermost div wrapper
         * that contains this field label and field element (the default class is 'x-form-item' and itemCls
         * will be added to that). If supplied, itemCls at the field level will override the default itemCls
         * supplied at the container level.
         * id : StringThe id of the Field
         * {@link #labelStyle} : String
         * A CSS style specification string to add to the field label for this field (defaults to '' or the
         * {@link #labelStyle layout's value for labelStyle}).
         * label : StringThe text to display as the label for this
         * field (defaults to the field's configured fieldLabel property)
         * {@link #labelSeparator} : StringThe separator to display after
         * the text of the label for this field (defaults to a colon ':' or the
         * {@link #labelSeparator layout's value for labelSeparator}). To hide the separator use empty string ''.
         * elementStyle : StringThe styles text for the input element's wrapper.
         * clearCls : StringThe CSS class to apply to the special clearing div
         * rendered directly after each form field wrapper (defaults to 'x-form-clear-left')
         *
         * @param (Ext.form.Field} field The {@link Ext.form.Field Field} being rendered.
         * @return {Object} An object hash containing the properties required to render the Field.
         */
        getTemplateArgs: function(field) {
            var noLabelSep = !field.fieldLabel || field.hideLabel;

            return {
                id            : field.id,
                label         : field.fieldLabel,
                itemCls       : (field.itemCls || this.container.itemCls || '') + (field.hideLabel ? ' x-hide-label' : ''),
                clearCls      : field.clearCls || 'x-form-clear-left',
                labelStyle    : this.getLabelStyle(field.labelStyle),
                elementStyle  : this.elementStyle || '',
                labelSeparator: noLabelSep ? '' : (Ext.isDefined(field.labelSeparator) ? field.labelSeparator : this.labelSeparator)
            };
        },

        // private
        adjustWidthAnchor: function(value, c){
            if(c.label && !this.isHide(c) && (this.container.labelAlign != 'top')){
                var adjust = Ext.isIE6 || (Ext.isIE && !Ext.isStrict);
                return value - this.labelAdjust + (adjust ? -3 : 0);
            }
            return value;
        },

        adjustHeightAnchor : function(value, c){
            if(c.label && !this.isHide(c) && (this.container.labelAlign == 'top')){
                return value - c.label.getHeight();
            }
            return value;
        },

        // private
        isValidParent : function(c, target){
            return target && this.container.getEl().contains(c.getPositionEl());
        }

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

    Ext.Container.LAYOUTS['form'] = Ext.layout.FormLayout;