code: private Set<VarBindingDef> getPropertyProviders( Set<String> properties)
      {
      Set<VarBindingDef> bindings = new HashSet<VarBindingDef>();
      for( String property : properties)
        {
        bindings.addAll( propertyProviders_.get( property));
        }
  
      return bindings;
      }
docs: Returns the set of bindings that provide at least one of the given properties