StkInst Documentation Example Not Working?

I was looking into this here:

I copied the examples into supercollider, evaluated, and got this error message:
ERROR: Class not defined.
in interpreted text
line 5 char 17:

  sig ="Mandolin"),freq, gate, amp, 0.5)*env;
        , sig.dup);

sig is written in the SynthDef as a variable. I am baffled why this isn’t working.

Do you have the sc3plugins installed? Seems like StkInst is part of that.

Where would I find the download for those?

I think I found the download here:
Is there a place that the folder needs to be in order for Supercollider to access it, because I’m still seeing the errors.

In Scide, in File menu, click “Open user support directory”. In the folder that opens, create an Extensions subfolder if it doesn’t exist already. That is where my plugins are installed.

To make sure that supercollider finds your plugins, just after installing the plugins be sure to quit scide and restart it (this is needed only once).