Library code that's ok to use by external applications (e.g., /pkg/mypubliclib).
Other projects will import these libraries expecting them to work, so think twice before you put something here :-)
Note that the internal directory is a better way to ensure your private packages are not importable because
it's enforced by Go. The /pkg directory is still a good way to explicitly communicate that the code in that directory
is safe for use by others. The I'll take pkg over internal blog post by Travis Jeffery provides a good overview
of the pkg and internal directories and when it might make sense to use them.