anchor.diff:  sourceElement
    : statement
    | functionDeclaration
  + | importDeclaration
  + | exportDeclaration
  + | lexicalDeclaration
  + | classDeclaration
    ;
   
   /// Statement :
  
positive.code:  | throwStatement
   | tryStatement
   | debuggerStatement
   | importStatement
   | exportStatement
   | lexicalStatement
   ;
  
  lexicalStatement
    : 'let' bindingList
    | 'const' bindingList
  ;
  
  bindingList
  
negative.code:   : '...' Identifier
  ;
  
  importDeclaration
   : Import importClause fromClause ';'?
   | Import StringLiteral ';'?
  ;
  
  
  