http://webwork.maa.org/wiki/Scaffold#.WBj2Dcn9g1A
which I thought was sufficient to start.
Now that you mention the descriptions, I searched and found
https://github.com/openwebwork/pg/blob/master/macros/scaffold.pl
which contains the text you quote.
I plead guilty to not going deep enough, and I thank you for indicating that I should actually read the macros before using them, which I rarely do.
thanks