code: public Tuple add( VarBindingDef binding)
      {
      if( binding != null)
        {
        VarDef var = binding.getVarDef();
        if( var == null)
          {
          throw new IllegalArgumentException( "Invalid binding=" + binding + ": variable undefined");
          }
  
        VarValueDef value = binding.getValueDef();
        if( value == null)
          {
          throw new IllegalArgumentException( "Invalid binding=" + binding + ": value undefined");
          }
        
        remove( var);
  
        bindings_.put( var, binding);
        properties_.addAll( value.getProperties().iterator());
        }
  
      return this;
      }
docs: Adds a binding to this tuple.