anchor.diff:      : expression
       ;
   
  -expressions_
  +expressions
       : expression (',' expression)*
       ;
   
  
positive.code: 
  pivot_in_clause_elements
      : expression
      | '(' expressions_? ')'
      ;
  
  unpivot_clause
  
negative.code:     ;
  
  cost_matrix_clause
      : COST (MODEL AUTO? | '(' cost_class_name (',' cost_class_name)* ')' VALUES '(' expressions? ')')
      ;
  
  xml_passing_clause
  