code: public void visitPubapi(Element e) {
          Name n = ((ClassSymbol)e).fullname;
          Name p = ((ClassSymbol)e).packge().fullname;
          StringBuffer sb = publicApiPerClass.get(n);
          assert(sb == null);
          sb = new StringBuffer();
          PubapiVisitor v = new PubapiVisitor(sb);
          v.visit(e);
          if (sb.length()>0) {
              publicApiPerClass.put(n, sb);
          }
          explicitPackages.add(p);
       }
docs: Visit the api of a class and construct a pubapi string and
  store it into the pubapi_perclass map.