Packages can also require other packages in order to work. These are called “indirect”, or transitive, dependencies. The package developer adds these dependencies to the package’s manifest during development. For example, there are several 2D packages that share functionality: both the 2D Animation and 2D Sprite Shape packages depend on the 2D Common package.
当您将包版本添加为依赖项时，该版本不一定是 Package Manager 安装的版本，因为它必须考虑项目中的所有依赖项，无论是直接的还是间接的。为了决定安装哪些包，Package Manager 构建了一个列表，列出每个直接和间接依赖项。