anchor.diff:  //    NonZeroDigit DecimalDigits[opt]
   fragment
   DecimalIntegerLiteral
  -: '0'
  -| NonZeroDigit DecimalDigits?
  +: ('0'|NonZeroDigit DecimalDigits?)
   ;
   
   // DecimalDigits::
  
positive.code: //    OctalIntegerLiteral
  //    HexIntegerLiteral
  NumericLiteral
  : DecimalLiteral
  | BinaryIntegerLiteral
  | OctalIntegerLiteral
  | HexIntegerLiteral
  ;
  
  // DecimalLiteral::
  
negative.code: // HexIntegerLiteral::
  //    0x HexDigits
  //    0X HexDigits
  fragment
  HexIntegerLiteral
  : '0' [xX] HexDigits
  ;
  
  // HexDigits::
  