anchor.diff:      ;
   
   user
  -    : STRING AT_ STRING
  -    | STRING
  -    | ID
  +    : STRING AT_ STRING | STRING | ID
       ;
   
   users
  
positive.code:     ;
  
  grantProxy
      : GRANT PROXY ON userOrRole
      TO userOrRoles
      (WITH GRANT OPTION)?
      ;
  
  grantRoles
      : GRANT roleNames
      TO userOrRoles
      (WITH ADMIN OPTION)?
      ;
  
  revokePriveleges
      : REVOKE
      privType columnList? (COMMA privType columnList?)*
      ON objectType? privLevel
      FROM userOrRoles
      ;
  
negative.code: import MySQLKeyword, Keyword, BaseRule, DataType, Symbol;
  
  grantPriveleges
      : GRANT privType columnList? (COMMA privType columnList?)*
      ON objectType? privLevel
      TO userOrRoles
      (WITH GRANT OPTION)?
  