<li>the statement lists in each case, including the default, end in a terminating
	    statement, or a possibly labeled <a href="#Fallthrough_statements">"fallthrough"
	    statement</a>.</li>
	</ul>
</li>

<li>
	A <a href="#Select_statements">"select" statement</a> in which:
	<ul>
	<li>there are no "break" statements referring to the "select" statement, and</li>

	<li>the statement lists in each case, including the default, end in a terminating
	    statement, or a possibly labeled <a href="#Fallthrough_statements">"fallthrough"
	    statement</a>.</li>
	</ul>
</li>

<li>
	A <a href="#Select_statements">"select" statement</a> in which:
	<ul>
	<li>there are no "break" statements referring to the "select" statement, and</li>

not the older version.

To override these defaults, a main package's source files
can include one or more `//go:debug` directives at the top of the file
(preceding the `package` statement).
Continuing the `panicnil` example, if the module or workspace is updated
to say `go` `1.21`, the program can opt back into the old `panic(nil)`
behavior by including this directive:

	//go:debug panicnil=1

/*
Implementation details.

Cgo provides a way for Go programs to call C code linked into the same
address space. This comment explains the operation of cgo.

Cgo reads a set of Go source files and looks for statements saying
import "C". If the import has a doc comment, that comment is
taken as literal C code to be used as a preamble to any C code
generated by cgo. A typical preamble #includes necessary definitions:

The completion of all <code>init</code> functions is synchronized before
the start of the function <code>main.main</code>.
</p>

<h3 id="go">Goroutine creation</h3>

<p class="rule">
The <code>go</code> statement that starts a new goroutine
is synchronized before the start of the goroutine's execution.
</p>

<p>
For example, in this program:
</p>

<pre>
var a string

func f() {
	print(a)
}