| errors | Package errors implements functions to manipulate errors. |
| os | Package os provides a platform-independent interface to operating system functionality. |
| path/filepath | Package filepath implements utility routines for manipulating filename paths in a way compatible with the target operating system-defined file paths. |
| regexp | Package regexp implements regular expression search. |
| strings | Package strings implements simple functions to manipulate UTF-8 encoded strings. |
| text/scanner | Package scanner provides a scanner and tokenizer for UTF-8-encoded text. |
| unicode/utf8 | Package utf8 implements functions and constants to support text encoded in UTF-8. |