Why are Some golang.org Packages Prefixed with an `x`
<p>Why are some golang.org package names prefixed with an <code>x</code>?  The specific package that piqued my interest <a href="https://godoc.org/golang.org/x/crypto" rel="noreferrer">was bycrypt</a></p>
<p>My main concern is the <code>x</code> means something like e<strong>X</strong>perimental, and I should use a different set of libraries if I want something stable.  If not that, the <code>x</code> is there to signify something -- I'm  curious what it is.</p>