anchor.diff:  //                U+202F    NARROW NO-BREAK SPACE
   //     <MMSP>     U+205F    MEDIUM MATHEMATICAL SPACE     &MediumSpace;
   //                U+3000    IDEOGRAPHIC SPACE
  -fragment WHITE_SPACE
  +fragment
  +WHITE_SPACE
   : [\t\u000b\u000c\u0020\u00a0\ufeff\u0085\u1680\u2000-\u200a\u202f\u205f\u3000]
   ;
   
  
positive.code: //     <LS>
  //     <PS>
  //     <CR><LF>
  LINE_TERMINATOR_SEQUENCE
  : '\r\n'
  | LINE_TERMINATOR
  ;
  
  // ref. Section 11.4
  
negative.code: //     SourceCharacter but not LineTerminator
  // Must be consistent with LINE_TERMINATOR, alas ~(LINE_TERMINATOR) syntax
  // is not supported by ANTLR4
  fragment
  SINGLE_LINE_COMMENT
  : '//' ~[\n\r\u2028\u2029]*
  ;
  