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