translate concept-aliases and autoloading [skip cii]

docs/guide-zh-CN/concept-aliases.md

+路径别名（Aliases）
+=======
+
+路径别名（Path Alias 简称别名）用作代表文件路径和 URL，主要为了避免在代码中硬编码一些绝对路径和 
+URL。一个别名必须以 `@` 字符开头，以区别于传统的文件/目录路径或 URL。举栗，别名 `@yii` 
+指的是 Yii 框架本身的安装目录，而 `@web` 表示的是当前运行应用的根 URL（base URL）。
+
+
+定义别名 <a name="defining-aliases"></a>
+----------------
+
+你可以调用 [[Yii::setAlias()]] 来给指定路径/URL 定义别名。栗子：
+
+```php
+// 文件路径的别名
+Yii::setAlias('@foo', '/path/to/foo');
+
+// URL 的别名
+Yii::setAlias('@bar', 'http://www.example.com');
+```
+
+> 注意：别名所指向的文件路径或 URL 不一定是真实存在的文件或资源哦。
+
+用一个别名，你能通过在后面接续斜杠 `/` 以及若干路径片段得到一个新的别名（无需调用 
+[[Yii::setAlias()]]）。我们把通过 [[Yii::setAlias()]] 定义的别名成为根别名 
+*root aliases*，而用他们衍生出去的别名成为衍生别名 *derived aliases*。比如，`@foo` 就是跟别名，而 `@foo/bar/file.php` 
+是一个衍生别名。
+
+你还可以用别名定义新别名（根别名与衍生别名均可）：
+
+```php
+Yii::setAlias('@foobar', '@foo/bar');
+```
+
+根别名通常在 [引导（bootstrapping）](runtime-bootstrapping.md) 阶段定义。比如你可以在 
+[入口脚本](structure-entry-scripts.md) 里调用 [[Yii::setAlias()]]。为了方便起见呢，[应用主体（Application）](structure-applications.md) 
+提供了一个名为 `aliases` 的可写属性，你可以在应用[配置文件](concept-configurations.md)中设置它，就像这样：
+
+```php
+return [
+    // ...
+    'aliases' => [
+        '@foo' => '/path/to/foo',
+        '@bar' => 'http://www.example.com',
+    ],
+];
+```
+
+
+解析别名 <a name="resolving-aliases"></a>
+-----------------
+
+你可以调用 [[Yii::getAlias()]] 命令来解析一个根别名到他所对应的文件路径或 URL。同样的页面也可以用于解析衍生别名。比如：
+
+```php
+echo Yii::getAlias('@foo');               // 显示：/path/to/foo
+echo Yii::getAlias('@bar');               // 显示：http://www.example.com
+echo Yii::getAlias('@foo/bar/file.php');  // 显示：/path/to/foo/bar/file.php
+```
+
+由衍生别名所代指的路径/URL 是通过替换掉衍生别名中的根别名部分得到的。
+
+> 注意：[[Yii::getAlias()]] 不检查结果路径/URL 所指向的资源是否真实存在。
+
+根别名可能也会包含斜杠 `/` 字符。[[Yii::getAlias()]] 足够聪明，能知道一个别名中的哪个部分是根别名，因此能正确解析文件路径/URL。比如：
+
+```php
+Yii::setAlias('@foo', '/path/to/foo');
+Yii::setAlias('@foo/bar', '/path2/bar');
+Yii::getAlias('@foo/test/file.php');  // 显示：/path/to/foo/test/file.php
+Yii::getAlias('@foo/bar/file.php');   // 显示：/path2/bar/file.php
+```
+
+若 `@foo/bar` 未被定义为根别名，最后一行语句会显示为 `/path/to/foo/bar/file.php`。
+
+
+使用别名 <a name="using-aliases"></a>
+-------------
+
+别名在 Yii 的很多地方都会被正确识别，而无需调用 [[Yii::getAlias()]] 
+来把它们转换为路径/URL。比如，[[yii\caching\FileCache::cachePath]] 能同时接受文件路径或是代表文件路径的别名，多亏了 `@` 前缀，它区分开了文件路径与别名。
+
+```php
+use yii\caching\FileCache;
+
+$cache = new FileCache([
+    'cachePath' => '@runtime/cache',
+]);
+```
+
+请关注下 API 文档了解属性或方法参数是否支持别名。
+
+
+预定义的别名 <a name="predefined-aliases"></a>
+------------------
+
+Yii 预定义了一系列别名来简化频繁引用常用路径和 URL的需求。
+在核心框架中已经预定义有以下别名：
+
+- `@yii` - `BaseYii.php` 文件所在的目录（也被称为框架安装目录）
+- `@app` - 当前运行的应用 [[yii\base\Application::basePath|根路径（base path）]] 
+- `@runtime` - 当前运行的应用的 [[yii\base\Application::runtimePath|运行环境（runtime）路径]] 
+- `@vendor` - [[yii\base\Application::vendorPath|Composer 供应商目录]]
+- `@webroot` - 当前运行应用的 Web 入口目录
+- `@web` - 当前运行应用的根 URL
+
+`@yii` 别名是在[入口脚本](structure-entry-scripts.md)里包含 `Yii.php` 文件时定义的，其他的别名都是在[配置应用](concept-configurations.md)的时候，于应用的构造器内定义的。
+
+
+扩展的别名 <a name="extension-aliases"></a>
+-----------------
+
+每一个通过 Composer 安装的 [扩展](structure-extensions.md) 都自动添加了一个别名。该别名会以该扩展在 `composer.json` 
+文件中所声明的根命名空间为名，且他直接代指该包的根目录。比如，如果你安装有 `yiisoft/yii2-jui` 扩展，你会自动得到 
+`@yii/jui` 别名，它定义于[引导启动](runtime-bootstrapping.md)阶段：
+
+```php
+Yii::setAlias('@yii/jui', 'VendorPath/yiisoft/yii2-jui');
+```
\ No newline at end of file

docs/guide-zh-CN/concept-autoloading.md

+类自动加载（Autoloading）
+=================
+
+Yii relies on the [class autoloading mechanism](http://www.php.net/manual/en/language.oop5.autoload.php)
+to locate and include required class files. It provides a high-performance class autoloader that is compliant to the
+[PSR-4 标准](https://github.com/php-fig/fig-standards/blob/master/proposed/psr-4-autoloader/psr-4-autoloader.md).
+The autoloader is installed when you include the `Yii.php` file.
+
+> Note: For simplicity of description, in this section we will only talk about autoloading of classes. However, keep in
+  mind that the content we are describing here applies to autoloading of interfaces and traits as well.
+
+
+使用 Yii 自动加载器 <a name="using-yii-autoloader"></a>
+------------------------
+
+To make use of the Yii class autoloader, you should follow two simple rules when creating and naming your classes:
+
+* Each class must be under some namespace (e.g. `foo\bar\MyClass`).
+* Each class must be saved in an individual file whose path is determined by the following algorithm:
+
+```php
+// $className is a fully qualified class name with the leading backslash
+$classFile = Yii::getAlias('@' . str_replace('\\', '/', $className) . '.php');
+```
+
+For example, if a class name is `foo\bar\MyClass`, the [alias](concept-aliases.md) for the corresponding class file path
+would be `@foo/bar/MyClass.php`. In order for this alias to be able to be resolved into a file path,
+either `@foo` or `@foo/bar` must be a [root alias](concept-aliases.md#defining-aliases).
+
+When you are using the [Basic Application Template](start-basic.md), you may put your classes under the top-level
+namespace `app` so that they can be autoloaded by Yii without the need of defining a new alias. This is because
+`@app` is a [predefined alias](concept-aliases.md#predefined-aliases), and a class name like `app\components\MyClass`
+can be resolved into the class file `AppBasePath/components/MyClass.php`, according to the algorithm we just described.
+
+In the [Advanced Application Template](tutorial-advanced-app.md), each tier has its own root alias. For example,
+the front-end tier has a root alias `@frontend` while the back-end tier `@backend`. As a result, you may
+put the front-end classes under the namespace `frontend` while the back-end classes under `backend`. This will
+allow these classes to be autoloaded by the Yii autoloader.
+
+
+类映射表（Class Map） <a name="class-map"></a>
+---------
+
+The Yii class autoloader supports the *class map* feature which maps class names to the corresponding class file paths.
+When the autoloader is loading a class, it will first check if the class is found in the map. If so, the corresponding
+file path will be included directly without further check. This makes class autoloading super fast. In fact,
+all core Yii classes are being autoloaded this way.
+
+You may add a class to the class map `Yii::$classMap` as follows,
+
+```php
+Yii::$classMap['foo\bar\MyClass'] = 'path/to/MyClass.php';
+```
+
+[Aliases](concept-aliases.md) can be used to specify class file paths. You should set the class map in the
+[bootstrapping](runtime-bootstrapping.md) process so that the map is ready before your classes are used.
+
+
+用其他自动加载器 <a name="using-other-autoloaders"></a>
+-----------------------
+
+Because Yii embraces Composer as a package dependency manager, it is recommended that you also install
+the Composer autoloader. If you are using some 3rd-party libraries that have their autoloaders, you should
+also install them.
+
+When you are using the Yii autoloader together with other autoloaders, you should include the `Yii.php` file
+*after* all other autoloaders are installed. This will make the Yii autoloader to be the first one responding to
+any class autoloading request. For example, the following code is extracted from
+the [entry script](structure-entry-scripts.md) of the [Basic Application Template](start-basic.md). The first
+line installs the Composer autoloader, while the second line installs the Yii autoloader.
+
+```php
+require(__DIR__ . '/../vendor/autoload.php');
+require(__DIR__ . '/../vendor/yiisoft/yii2/Yii.php');
+```
+
+You may use the Composer autoloader alone without the Yii autoloader. However, by doing so, the performance
+of your class autoloading may be degraded, and you must follow the rules set by Composer in order for your classes
+to be autoloadable.
+
+> Info: If you do not want to use the Yii autoloader, you must create your own version of the `Yii.php` file
+  and include it in your [entry script](structure-entry-scripts.md).
+
+
+自动加载扩展类 <a name="autoloading-extension-classes"></a>
+-----------------------------
+
+The Yii autoloader is capable of autoloading [extension](structure-extensions.md) classes. The sole requirement
+is that an extension specifies the `autoload` section correctly in its `composer.json` file. Please refer to the
+[Composer documentation](https://getcomposer.org/doc/04-schema.md#autoload) for more details about specifying `autoload`.
+
+In case you do not use the Yii autoloader, the Composer autoloader can still autoload extension classes for you.