To install:

1) chrome://extensions/
2) click "[+] Developer Mode" in top right
3) "Load unpacked extension..."
4) pick $GOROOT/misc/chrome/gophertool

programs listing versions of Go earlier than Go 1.20 are configured to match Go 1.20,
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: