Mention if ~s "..." needs quotes

[積丹尼 Dan Jacobson]

In (info "(mailutils) Modifying the Headers")

   To change the 'Subject' header, use '~s' escape, e.g.:

     ~s "Re: your message"

Mention if one can also just use

     ~s Re: your message

without the quotes or not, and also how to get a real quote mark into the 
Subject.