| context | Package context defines the Context type, which carries deadlines, cancellation signals, and other request-scoped values across API boundaries and between processes. |
| errors | Package errors implements functions to manipulate errors. |
| reflect | Package reflect implements run-time reflection, allowing a program to manipulate objects with arbitrary types. |
| strings | Package strings implements simple functions to manipulate UTF-8 encoded strings. |
| testing | Package testing provides support for automated testing of Go packages. |
| time | Package time provides functionality for measuring and displaying time. |