Understanding "help" command description syntax - explanation needed

[Darren Chen]

在 2014年11月5日星期三UTC+8下午8时17分11秒，Larry.... at gmail.com写道：
> On Wed, Nov 5, 2014 at 7:13 AM, Ivan Evstegneev <webmailgroups at gmail.com> wrote:
> > Firtst of all thanks for reply.
> >
> >>>brackets [] means that the argument is optional.
> >
> > That's what I'm talking about (asking actually), where do you know it from?
> 
> I know it because I've been a programmer for 39 years.

that's awesome！！