Source of packages.
| Unknown | The package source is unknown. |
| Registry | The package is from a registry. |
| BuiltIn | The package is built-in and part of Unity. |
| Embedded | The package is embedded in the Unity project. |
| Local | The package is referenced by a local path. |
| Git | The package is referenced directly by a Git URL. |
| LocalTarball | The package is referenced by a local path pointing to a GZip tarball file. |