fmt package.
++The standard library's purpose is to support the runtime, connect to +the operating system, and provide key functionality that many Go +programs require, such as formatted I/O and networking. +It also contains elements important for web programming, including +cryptography and support for standards like HTTP, JSON, and XML. +
+ ++There is no clear criterion that defines what is included because for +a long time, this was the only Go library. +There are criteria that define what gets added today, however. +
+ ++New additions to the standard library are rare and the bar for +inclusion is high. +Code included in the standard library bears a large ongoing maintenance cost +(often borne by those other than the original author), +is subject to the Go 1 compatibility promise +(blocking fixes to any flaws in the API), +and is subject to the Go +release schedule, +preventing bug fixes from being available to users quickly. +
+ +
+Most new code should live outside of the standard library and be accessible
+via the go tool's
+go get command.
+Such code can have its own maintainers, release cycle,
+and compatibility guarantees.
+Users can find packages and read their documentation at
+godoc.org.
+
+Although there are pieces in the standard library that don't really belong,
+such as log/syslog, we continue to maintain everything in the
+library because of the Go 1 compatibility promise.
+But we encourage most new code to live elsewhere.
+