anchor.diff:  
   element_separator :
        COMMA
  +  |  {isElementSeparator()}? FILLER
     ;
   
   input_params :
  
positive.code: 
  primary_expr :
       literal
    |  LPAREN FILLER? expr RPAREN
    |  matrix
    |  cell_array
    |  access
  
negative.code: //AC: keep the lexer and the parser together for now because that's the default Antlr layout
  
  options {
      output = template;
      rewrite = true;
  }
  
  @parser::header {
  