code: void mapIn(String in, Object comp, String comp_in) {
          if (comp == ca.getComponent()) {
              throw new ComponentException("cannot connect 'In' with itself for " + in);
          }
          ComponentAccess ac_dest = lookup(comp);
          FieldAccess destAccess = (FieldAccess) ac_dest.input(comp_in);
          checkFA(destAccess, comp, comp_in);
          FieldAccess srcAccess = (FieldAccess) ca.input(in);
          checkFA(srcAccess, ca.getComponent(), in);
  
          FieldContent data = srcAccess.getData();
          data.tagLeaf();
          data.tagIn();
  
          destAccess.setData(data);
          dataSet.add(data);
          if (log.isLoggable(Level.CONFIG)) {
              log.config(String.format("@In(%s) -> @In(%s)", srcAccess, destAccess));
          }
  //        ens.fireMapIn(srcAccess, destAccess);
      }
docs: Map two input fields.
  
  @param in
  @param comp
  @param comp_in