code: protected void writeFunction( FunctionInputDef function)
      {
      xmlWriter_
        .element( FUNCTION_TAG)
        .attribute( NAME_ATR, function.getName())
        .content( () ->
          {
          writeAnnotations( function);
          for( String varType : function.getVarTypes())
            {
            writeInputs(
              varType,
              toStream( function.getVarDefs())
              .filter( varDef -> varDef.getType().equals( varType))
              .sorted());
            }
          })
        .write();
      }
docs: Writes the given function input definition.