The source code

    /**
     * @class Ext.Editor
     * @extends Ext.Component
     * A base editor field that handles displaying/hiding on demand and has some built-in sizing and event handling logic.
     * @constructor
     * Create a new Editor
     * @param {Object} config The config object
     * @xtype editor
     */
    Ext.Editor = function(field, config){
        if(field.field){
            this.field = Ext.create(field.field, 'textfield');
            config = Ext.apply({}, field); // copy so we don't disturb original config
            delete config.field;
        }else{
            this.field = field;
        }
        Ext.Editor.superclass.constructor.call(this, config);
    };

    Ext.extend(Ext.Editor, Ext.Component, {
        /**
        * @cfg {Ext.form.Field} field
        * The Field object (or descendant) or config object for field
        */
        /**
         * @cfg {Boolean} allowBlur
         * True to {@link #completeEdit complete the editing process} if in edit mode when the
         * field is blurred. Defaults to <tt>true</tt>.
         */
        allowBlur: true,
        /**
         * @cfg {Boolean/String} autoSize
         * True for the editor to automatically adopt the size of the underlying field, "width" to adopt the width only,
         * or "height" to adopt the height only, "none" to always use the field dimensions. (defaults to false)
         */
        /**
         * @cfg {Boolean} revertInvalid
         * True to automatically revert the field value and cancel the edit when the user completes an edit and the field
         * validation fails (defaults to true)
         */
        /**
         * @cfg {Boolean} ignoreNoChange
         * True to skip the edit completion process (no save, no events fired) if the user completes an edit and
         * the value has not changed (defaults to false).  Applies only to string values - edits for other data types
         * will never be ignored.
         */
        /**
         * @cfg {Boolean} hideEl
         * False to keep the bound element visible while the editor is displayed (defaults to true)
         */
        /**
         * @cfg {Mixed} value
         * The data value of the underlying field (defaults to "")
         */
        value : "",
        /**
         * @cfg {String} alignment
         * The position to align to (see {@link Ext.Element#alignTo} for more details, defaults to "c-c?").
         */
        alignment: "c-c?",
        /**
         * @cfg {Array} offsets
         * The offsets to use when aligning (see {@link Ext.Element#alignTo} for more details. Defaults to <tt>[0, 0]</tt>.
         */
        offsets: [0, 0],
        /**
         * @cfg {Boolean/String} shadow "sides" for sides/bottom only, "frame" for 4-way shadow, and "drop"
         * for bottom-right shadow (defaults to "frame")
         */
        shadow : "frame",
        /**
         * @cfg {Boolean} constrain True to constrain the editor to the viewport
         */
        constrain : false,
        /**
         * @cfg {Boolean} swallowKeys Handle the keydown/keypress events so they don't propagate (defaults to true)
         */
        swallowKeys : true,
        /**
         * @cfg {Boolean} completeOnEnter True to complete the edit when the enter key is pressed. Defaults to <tt>true</tt>.
         */
        completeOnEnter : true,
        /**
         * @cfg {Boolean} cancelOnEsc True to cancel the edit when the escape key is pressed. Defaults to <tt>true</tt>.
         */
        cancelOnEsc : true,
        /**
         * @cfg {Boolean} updateEl True to update the innerHTML of the bound element when the update completes (defaults to false)
         */
        updateEl : false,

        initComponent : function(){
            Ext.Editor.superclass.initComponent.call(this);
            this.addEvents(
                /**
                 * @event beforestartedit
                 * Fires when editing is initiated, but before the value changes.  Editing can be canceled by returning
                 * false from the handler of this event.
                 * @param {Editor} this
                 * @param {Ext.Element} boundEl The underlying element bound to this editor
                 * @param {Mixed} value The field value being set
                 */
                "beforestartedit",
                /**
                 * @event startedit
                 * Fires when this editor is displayed
                 * @param {Ext.Element} boundEl The underlying element bound to this editor
                 * @param {Mixed} value The starting field value
                 */
                "startedit",
                /**
                 * @event beforecomplete
                 * Fires after a change has been made to the field, but before the change is reflected in the underlying
                 * field.  Saving the change to the field can be canceled by returning false from the handler of this event.
                 * Note that if the value has not changed and ignoreNoChange = true, the editing will still end but this
                 * event will not fire since no edit actually occurred.
                 * @param {Editor} this
                 * @param {Mixed} value The current field value
                 * @param {Mixed} startValue The original field value
                 */
                "beforecomplete",
                /**
                 * @event complete
                 * Fires after editing is complete and any changed value has been written to the underlying field.
                 * @param {Editor} this
                 * @param {Mixed} value The current field value
                 * @param {Mixed} startValue The original field value
                 */
                "complete",
                /**
                 * @event canceledit
                 * Fires after editing has been canceled and the editor's value has been reset.
                 * @param {Editor} this
                 * @param {Mixed} value The user-entered field value that was discarded
                 * @param {Mixed} startValue The original field value that was set back into the editor after cancel
                 */
                "canceledit",
                /**
                 * @event specialkey
                 * Fires when any key related to navigation (arrows, tab, enter, esc, etc.) is pressed.  You can check
                 * {@link Ext.EventObject#getKey} to determine which key was pressed.
                 * @param {Ext.form.Field} this
                 * @param {Ext.EventObject} e The event object
                 */
                "specialkey"
            );
        },

        // private
        onRender : function(ct, position){
            this.el = new Ext.Layer({
                shadow: this.shadow,
                cls: "x-editor",
                parentEl : ct,
                shim : this.shim,
                shadowOffset: this.shadowOffset || 4,
                id: this.id,
                constrain: this.constrain
            });
            if(this.zIndex){
                this.el.setZIndex(this.zIndex);
            }
            this.el.setStyle("overflow", Ext.isGecko ? "auto" : "hidden");
            if(this.field.msgTarget != 'title'){
                this.field.msgTarget = 'qtip';
            }
            this.field.inEditor = true;
            this.mon(this.field, {
                scope: this,
                blur: this.onBlur,
                specialkey: this.onSpecialKey
            });
            if(this.field.grow){
                this.mon(this.field, "autosize", this.el.sync,  this.el, {delay:1});
            }
            this.field.render(this.el).show();
            this.field.getEl().dom.name = '';
            if(this.swallowKeys){
                this.field.el.swallowEvent([
                    'keypress', // *** Opera
                    'keydown'   // *** all other browsers
                ]);
            }
        },

        // private
        onSpecialKey : function(field, e){
            var key = e.getKey(),
                complete = this.completeOnEnter && key == e.ENTER,
                cancel = this.cancelOnEsc && key == e.ESC;
            if(complete || cancel){
                e.stopEvent();
                if(complete){
                    this.completeEdit();
                }else{
                    this.cancelEdit();
                }
                if(field.triggerBlur){
                    field.triggerBlur();
                }
            }
            this.fireEvent('specialkey', field, e);
        },

        /**
         * Starts the editing process and shows the editor.
         * @param {Mixed} el The element to edit
         * @param {String} value (optional) A value to initialize the editor with. If a value is not provided, it defaults
          * to the innerHTML of el.
         */
        startEdit : function(el, value){
            if(this.editing){
                this.completeEdit();
            }
            this.boundEl = Ext.get(el);
            var v = value !== undefined ? value : this.boundEl.dom.innerHTML;
            if(!this.rendered){
                this.render(this.parentEl || document.body);
            }
            if(this.fireEvent("beforestartedit", this, this.boundEl, v) !== false){
                this.startValue = v;
                this.field.reset();
                this.field.setValue(v);
                this.realign(true);
                this.editing = true;
                this.show();
            }
        },

        // private
        doAutoSize : function(){
            if(this.autoSize){
                var sz = this.boundEl.getSize(),
                    fs = this.field.getSize();

                switch(this.autoSize){
                    case "width":
                        this.setSize(sz.width, fs.height);
                        break;
                    case "height":
                        this.setSize(fs.width, sz.height);
                        break;
                    case "none":
                        this.setSize(fs.width, fs.height);
                        break;
                    default:
                        this.setSize(sz.width, sz.height);
                }
            }
        },

        /**
         * Sets the height and width of this editor.
         * @param {Number} width The new width
         * @param {Number} height The new height
         */
        setSize : function(w, h){
            delete this.field.lastSize;
            this.field.setSize(w, h);
            if(this.el){
                // IE7 in strict mode doesn't size properly.
                if(Ext.isGecko2 || Ext.isOpera || (Ext.isIE7 && Ext.isStrict)){
                    // prevent layer scrollbars
                    this.el.setSize(w, h);
                }
                this.el.sync();
            }
        },

        /**
         * Realigns the editor to the bound field based on the current alignment config value.
         * @param {Boolean} autoSize (optional) True to size the field to the dimensions of the bound element.
         */
        realign : function(autoSize){
            if(autoSize === true){
                this.doAutoSize();
            }
            this.el.alignTo(this.boundEl, this.alignment, this.offsets);
        },

        /**
         * Ends the editing process, persists the changed value to the underlying field, and hides the editor.
         * @param {Boolean} remainVisible Override the default behavior and keep the editor visible after edit (defaults to false)
         */
        completeEdit : function(remainVisible){
            if(!this.editing){
                return;
            }
            // Assert combo values first
            if (this.field.assertValue) {
                this.field.assertValue();
            }
            var v = this.getValue();
            if(!this.field.isValid()){
                if(this.revertInvalid !== false){
                    this.cancelEdit(remainVisible);
                }
                return;
            }
            if(String(v) === String(this.startValue) && this.ignoreNoChange){
                this.hideEdit(remainVisible);
                return;
            }
            if(this.fireEvent("beforecomplete", this, v, this.startValue) !== false){
                v = this.getValue();
                if(this.updateEl && this.boundEl){
                    this.boundEl.update(v);
                }
                this.hideEdit(remainVisible);
                this.fireEvent("complete", this, v, this.startValue);
            }
        },

        // private
        onShow : function(){
            this.el.show();
            if(this.hideEl !== false){
                this.boundEl.hide();
            }
            this.field.show().focus(false, true);
            this.fireEvent("startedit", this.boundEl, this.startValue);
        },

        /**
         * Cancels the editing process and hides the editor without persisting any changes.  The field value will be
         * reverted to the original starting value.
         * @param {Boolean} remainVisible Override the default behavior and keep the editor visible after
         * cancel (defaults to false)
         */
        cancelEdit : function(remainVisible){
            if(this.editing){
                var v = this.getValue();
                this.setValue(this.startValue);
                this.hideEdit(remainVisible);
                this.fireEvent("canceledit", this, v, this.startValue);
            }
        },

        // private
        hideEdit: function(remainVisible){
            if(remainVisible !== true){
                this.editing = false;
                this.hide();
            }
        },

        // private
        onBlur : function(){
            // selectSameEditor flag allows the same editor to be started without onBlur firing on itself
            if(this.allowBlur === true && this.editing && this.selectSameEditor !== true){
                this.completeEdit();
            }
        },

        // private
        onHide : function(){
            if(this.editing){
                this.completeEdit();
                return;
            }
            this.field.blur();
            if(this.field.collapse){
                this.field.collapse();
            }
            this.el.hide();
            if(this.hideEl !== false){
                this.boundEl.show();
            }
        },

        /**
         * Sets the data value of the editor
         * @param {Mixed} value Any valid value supported by the underlying field
         */
        setValue : function(v){
            this.field.setValue(v);
        },

        /**
         * Gets the data value of the editor
         * @return {Mixed} The data value
         */
        getValue : function(){
            return this.field.getValue();
        },

        beforeDestroy : function(){
            Ext.destroyMembers(this, 'field');

            delete this.parentEl;
            delete this.boundEl;
        }
    });
    Ext.reg('editor', Ext.Editor);