Missing context from Error Handling section of The Book

[jbcden]

In the Adding Functionality section of the Error Handling guide, a line with args.flag_quiet is referenced. This is not a standard method and after doing some googling I found this post. It would seem a few sections regarding the creation of a custom Args struct were removed or left out by mistake. Either way, I'm not sure if this those sections should be re-added or if this section needs to be reworked without that struct.