Unity 概念
本节介绍有关 Unity Package Manager 功能的许多概念：
版本
Multiple versions of each package are available, marking changes to that package along its life cycle. Every time a developer updates the package, they give it a new version number. A change in package version tells you whether it contains a breaking change (major), new backward-compatible functionality (minor), or bug fixes only (patch), following Semantic Versioning.
要查看特定包可用的版本列表，请参阅查找特定版本。
清单
清单文件有两种类型：
- Project manifests (
manifest.json) store information that the Package Manager needs to locate and load the right packages, including a list of packages and versions declared as dependencies. - Package manifests (
package.json) store information about a specific package, and a list of packages and versions that the package requires.
这两种文件都使用 JSON（JavaScript 对象表示法）语法。
注册表
In the domain of Unity’s Package Manager, a package registry is a server that stores package contents and information (metadata) on each package version. Unity maintains a central registry of official packages that are available for distribution. By default, all projects use the official Unity package registry, but you can add addition al registries to store and distribute private packages or stage packages in development.
包管理
Unity Package Manager 是管理整个包系统的工具。此工具的主要任务包括：
- It communicates with the Unity package registry server and any additional registries you specify.
- 读取您的项目清单并获取包内容和元数据。
- It installs, upgrades, and uninstalls packages, whether they are dependencies of the project or one of the installed packages.
- It imports Asset Store packages that you previously downloaded or purchased.
- It enables and disables Unity’s built-in packages.
- It displays information about every version of every package.
- 当项目及其中的包需要多个包版本时解决冲突。
The Unity Package Manager installs samples, tools, and assets on a per-project basis, rather than installing them across all projects for a specific machine or device. It uses a global cache to store downloaded package metadata and contents. Once installed in a project, Unity treats package assets just like any other asset in the project, except that these assets are stored inside the package folder and are immutable. You can only permanently change content from Local and Embedded package sources.
包来源
来源描述了包的来源：
| 来源 | 描述 |
|---|---|
| 注册表 | The Unity Package Manager downloads most packages from a package registry server into a global cache on your computer as you request them. These packages are immutable, so you can use them in your project, but you cannot modify them or change their package manifests. |
| 内置 | 这些包允许您启用或禁用 Unity 功能（例如，地形物理 (Terrain Physics)、动画 (Animation) 等）。这些包是不可变的。有关更多信息，请参阅内置包。 |
| 嵌入式 | 项目文件夹中存储的所有包均为嵌入式。此来源与开发中状态相对应，因为当您开始新包的开发时，通常会将包所需的所有脚本、库、示例和其他资源放在项目文件夹下的文件夹中。 |
| 本地 | You can install a package from any folder on your computer (for example, if you have cloned a development repository locally). |
| Tarball (local) | You can install a package from a tarball file on your computer. The Package Manager extracts the package from the tarball and stores it in the cache. However, these packages are immutable, unlike installations from a local folder. |
| Git | The Package Manager installs Git-based packages directly from a Git repository instead of from the package registry server. |
要编辑包的包清单，请参阅检查包。
The Package Manager window displays a tag that corresponds to some of these sources. For more information, see Tags.