title: What are the meaning of template parameters A, B of std::multiset<A,B> respectively, and how does it work?
body: <p>I have asked in another question about <strong>std::multiset</strong>, but now I see I need a decent understanding and cannot find any more complicated example in the internet.</p>
  <p>Can you explain to me, maybe exemplarize, how <code>std::multiset&lt;A,B&gt;</code> works and what function is here of A and of B, and also if any of those can be omitted? Can I put A or B to some variable?
  I'd really appreciate some short example, or reference,</p>