Extending Yii

Code style

Extension code style SHOULD be similar to core framework code style.
In case of using getter and setter for defining a property it's preferred to use method in extension code rather than property.
All classes, methods and properties SHOULD be documented using phpdoc. Note that you can use markdown and link to properties and methods using the following syntax: e.g. [[name()]], [[name\space\MyClass::name()]].
If you're displaying errors to developers do not translate these (i.e. do not use \Yii::t()). Errors should be translated only if they're displayed to end users.
Extension SHOULD NOT use class prefixes (i.e. TbNavBar, EMyWidget, etc.)

Extension SHOULD provide a valid PSR-0 autoloading configuration in composer.json

Example 1: Code in repository root

./Class.php

"autoload": {
    "psr-0": { "vendor\\package\\": "" }
},

Example 2: Code in repository subfolder ./src

./src/vendor/package/Class.php

"autoload": {
    "psr-0": { "vendor\\package\\": "./src" }
},

Extension MUST use the type yii2-extension in composer.json file.
Extension MUST NOT use yii or yii2 in the composer package name or in the namespaces used in the package.
Extension SHOULD use namespaces in this format vendor-name\package (all lowercase).
Extension MAY use a yii2- prefix in the composer vendor name (URL).
Extension MAY use a yii2- prefix in the repository name (URL).

Additional code, eg. libraries, SHOULD be required in your composer.json file.
When extension is released in a stable version, its requirements SHOULD NOT include dev packages that do not have a stable release.
Use appropriate version constraints, eg. 1.*, @stable for requirements.

Extension SHOULD follow the rules of semantic versioning.
Use a consistent format for your repository tags, as they are treated as version strings by composer, eg. 0.2.4,0.2.5,0.3.0,1.0.0.

There should be a readme.md file clearly describing what extension does in English, its requirements, how to install and use it. It should be written using markdown. If you want to provide translated readme, name it as readme_ru.md where ru is your language code. If extension provides a widget it is a good idea to include some screenshots.
It is recommended to host your extensions at Github.
Extension MUST be registered at Packagist.
TBD: composer.json

If extension creates or modifies database schema always use Yii migrations instead of SQL files or custom scripts.
Migrations SHOULD be database agnostic.
You MUST NOT make use of active-record model classes in your migrations.

TBD

Extension SHOULD provide at least one message catalogue with either source or target language in English.
Extension MAY provide a configuration for creating message catalogues.

Auth-items for controllers SHOULD be named after the following format vendor\ext\controller\action.
Auth-items names may be shortened using an asterisk, eg. vendor\ext\*