The source code

    /**
     * @class Ext.data.Api
     * @extends Object
     * Ext.data.Api is a singleton designed to manage the data API including methods
     * for validating a developer's DataProxy API.  Defines variables for CRUD actions
     * create, read, update and destroy in addition to a mapping of RESTful HTTP methods
     * GET, POST, PUT and DELETE to CRUD actions.
     * @singleton
     */
    Ext.data.Api = (function() {

        // private validActions.  validActions is essentially an inverted hash of Ext.data.Api.actions, where value becomes the key.
        // Some methods in this singleton (e.g.: getActions, getVerb) will loop through actions with the code for (var verb in this.actions)
        // For efficiency, some methods will first check this hash for a match.  Those methods which do acces validActions will cache their result here.
        // We cannot pre-define this hash since the developer may over-ride the actions at runtime.
        var validActions = {};

        return {
            /**
             * Defined actions corresponding to remote actions:
             *
    actions: {
        create  : 'create',  // Text representing the remote-action to create records on server.
        read    : 'read',    // Text representing the remote-action to read/load data from server.
        update  : 'update',  // Text representing the remote-action to update records on server.
        destroy : 'destroy'  // Text representing the remote-action to destroy records on server.
    }
             *
             * @property actions
             * @type Object
             */
            actions : {
                create  : 'create',
                read    : 'read',
                update  : 'update',
                destroy : 'destroy'
            },

            /**
             * Defined {CRUD action}:{HTTP method} pairs to associate HTTP methods with the
             * corresponding actions for {@link Ext.data.DataProxy#restful RESTful proxies}.
             * Defaults to:
             *
    restActions : {
        create  : 'POST',
        read    : 'GET',
        update  : 'PUT',
        destroy : 'DELETE'
    },
             *
             */
            restActions : {
                create  : 'POST',
                read    : 'GET',
                update  : 'PUT',
                destroy : 'DELETE'
            },

            /**
             * Returns true if supplied action-name is a valid API action defined in {@link #actions} constants
             * @param {String} action
             * @param {String[]}(Optional) List of available CRUD actions.  Pass in list when executing multiple times for efficiency.
             * @return {Boolean}
             */
            isAction : function(action) {
                return (Ext.data.Api.actions[action]) ? true : false;
            },

            /**
             * Returns the actual CRUD action KEY "create", "read", "update" or "destroy" from the supplied action-name.  This method is used internally and shouldn't generally
             * need to be used directly.  The key/value pair of Ext.data.Api.actions will often be identical but this is not necessarily true.  A developer can override this naming
             * convention if desired.  However, the framework internally calls methods based upon the KEY so a way of retreiving the the words "create", "read", "update" and "destroy" is
             * required.  This method will cache discovered KEYS into the private validActions hash.
             * @param {String} name The runtime name of the action.
             * @return {String||null} returns the action-key, or verb of the user-action or null if invalid.
             * @nodoc
             */
            getVerb : function(name) {
                if (validActions[name]) {
                    return validActions[name];  // <-- found in cache.  return immediately.
                }
                for (var verb in this.actions) {
                    if (this.actions[verb] === name) {
                        validActions[name] = verb;
                        break;
                    }
                }
                return (validActions[name] !== undefined) ? validActions[name] : null;
            },

            /**
             * Returns true if the supplied API is valid; that is, check that all keys match defined actions
             * otherwise returns an array of mistakes.
             * @return {String[]||true}
             */
            isValid : function(api){
                var invalid = [];
                var crud = this.actions; // <-- cache a copy of the actions.
                for (var action in api) {
                    if (!(action in crud)) {
                        invalid.push(action);
                    }
                }
                return (!invalid.length) ? true : invalid;
            },

            /**
             * Returns true if the supplied verb upon the supplied proxy points to a unique url in that none of the other api-actions
             * point to the same url.  The question is important for deciding whether to insert the "xaction" HTTP parameter within an
             * Ajax request.  This method is used internally and shouldn't generally need to be called directly.
             * @param {Ext.data.DataProxy} proxy
             * @param {String} verb
             * @return {Boolean}
             */
            hasUniqueUrl : function(proxy, verb) {
                var url = (proxy.api[verb]) ? proxy.api[verb].url : null;
                var unique = true;
                for (var action in proxy.api) {
                    if ((unique = (action === verb) ? true : (proxy.api[action].url != url) ? true : false) === false) {
                        break;
                    }
                }
                return unique;
            },

            /**
             * This method is used internally by {@link Ext.data.DataProxy DataProxy} and should not generally need to be used directly.
             * Each action of a DataProxy api can be initially defined as either a String or an Object.  When specified as an object,
             * one can explicitly define the HTTP method (GET|POST) to use for each CRUD action.  This method will prepare the supplied API, setting
             * each action to the Object form.  If your API-actions do not explicitly define the HTTP method, the "method" configuration-parameter will
             * be used.  If the method configuration parameter is not specified, POST will be used.

    new Ext.data.HttpProxy({
        method: "POST",     // <-- default HTTP method when not specified.
        api: {
            create: 'create.php',
            load: 'read.php',
            save: 'save.php',
            destroy: 'destroy.php'
        }
    });

    // Alternatively, one can use the object-form to specify the API
    new Ext.data.HttpProxy({
        api: {
            load: {url: 'read.php', method: 'GET'},
            create: 'create.php',
            destroy: 'destroy.php',
            save: 'update.php'
        }
    });

             *
             * @param {Ext.data.DataProxy} proxy
             */
            prepare : function(proxy) {
                if (!proxy.api) {
                    proxy.api = {}; // <-- No api?  create a blank one.
                }
                for (var verb in this.actions) {
                    var action = this.actions[verb];
                    proxy.api[action] = proxy.api[action] || proxy.url || proxy.directFn;
                    if (typeof(proxy.api[action]) == 'string') {
                        proxy.api[action] = {
                            url: proxy.api[action]
                        };
                    }
                }
            },

            /**
             * Prepares a supplied Proxy to be RESTful.  Sets the HTTP method for each api-action to be one of
             * GET, POST, PUT, DELETE according to the defined {@link #restActions}.
             * @param {Ext.data.DataProxy} proxy
             */
            restify : function(proxy) {
                proxy.restful = true;
                for (var verb in this.restActions) {
                    proxy.api[this.actions[verb]].method = this.restActions[verb];
                }
                // TODO: perhaps move this interceptor elsewhere?  like into DataProxy, perhaps?  Placed here
                // to satisfy initial 3.0 final release of REST features.
                proxy.onWrite = proxy.onWrite.createInterceptor(function(action, o, response, rs) {
                    var reader = o.reader;
                    var res = {};
                    switch (response.status) {
                        case 200:   // standard 200 response, send control back to HttpProxy#onWrite
                            return true;
                            break;
                        case 201:   // entity created but no response returned
                            res[reader.meta.successProperty] = true;
                            break;
                        case 204:  // no-content.  Create a fake response.
                            res[reader.meta.successProperty] = true;
                            res[reader.meta.root] = null;
                            break;
                        default:
                            return true;
                            break;
                    }
                    if (res[reader.meta.successProperty] === true) {
                        this.fireEvent("write", this, action, res[reader.meta.root], res, rs, o.request.arg);
                    } else {
                        this.fireEvent('exception', this, 'remote', action, o, res, rs);
                    }
                    o.request.callback.call(o.request.scope, res[reader.meta.root], res, res[reader.meta.successProperty]);

                    return false;   // <-- false to prevent intercepted function from running.
                }, proxy);
            }
        };
    })();

    /**
     * @class Ext.data.Api.Error
     * @extends Ext.Error
     * Error class for Ext.data.Api errors
     */
    Ext.data.Api.Error = Ext.extend(Ext.Error, {
        constructor : function(message, arg) {
            this.arg = arg;
            Ext.Error.call(this, message);
        },
        name: 'Ext.data.Api'
    });
    Ext.apply(Ext.data.Api.Error.prototype, {
        lang: {
            'action-url-undefined': 'No fallback url defined for this action.  When defining a DataProxy api, please be sure to define an url for each CRUD action in Ext.data.Api.actions or define a default url in addition to your api-configuration.',
            'invalid': 'received an invalid API-configuration.  Please ensure your proxy API-configuration contains only the actions defined in Ext.data.Api.actions',
            'invalid-url': 'Invalid url.  Please review your proxy configuration.',
            'execute': 'Attempted to execute an unknown action.  Valid API actions are defined in Ext.data.Api.actions"'
        }
    });