anchor.diff:  
   level1Interval : (dateOrSeason | unknown) Slash (dateOrSeason | unknown | open);
   dateOrSeason
  -	: Year UASymbol?
  -	| Season UASymbol?
  -	| Year Dash Month UASymbol?
  -	| YearMonthDay UASymbol?
  +	: YearUA | Year
  +	| SeasonUA | Season
  +	| YearMonthUA | YearMonth
  +	| YearMonthDayUA | YearMonthDay
   	;
  -
  -//level1Interval
  -//	: Year UASymbol Slash Year
  -//	| Year Slash Year UASymbol
  -//	| Year UASymbol Slash Year UASymbol
  -//	| Year UASymbol Slash Year Dash Month
  -//	| Year Slash Year Dash Month UASymbol
  -//	| Year UASymbol Slash Year Dash Month UASymbol
  -//	| Season UASymbol Slash Season
   	
   
   // **************************   Level 2: Tokens   *************************** //
  
positive.code: Unknown : 'unknown';
  QuestionMarkTilde : '?~';
  
  Season : Year Dash ('21' | '22' | '23' | '24');
  UASymbol : QuestionMark | Tilde | QuestionMarkTilde;
  YearWithOneUnspecifedDigit : Digit Digit Digit U;
  
negative.code: 	| OpenParen Year CloseParen Dash MonthDay UASymbol
  	;
  YearKnownMonthDayUAParenUA : OpenParen YearKnownMonthDayUA CloseParen UASymbol;
  YearMonthKnownDayUA : YearMonth Dash OpenParen Day CloseParen UASymbol;
  YearMonthKnownDayUAParenUA : OpenParen YearMonthKnownDayUA CloseParen UASymbol;
  DayKnownYearMonthUA
  	: YearMonth UASymbol Dash Day
  	| Year UASymbol Dash Month UASymbol Dash Day
  	;
  DayKnownYearMonthUAParenUA : OpenParen DayKnownYearMonthUA CloseParen UASymbol;
  YearKnownMonthUA : Year Dash OpenParen Month CloseParen UASymbol;
  YearKnownMonthUAParenUA : OpenParen YearKnownMonthUA CloseParen UASymbol;
  Level2YearMonthUA : Year UASymbol Dash OpenParen Month CloseParen UASymbol;
  Level2YearMonthUAParenUA : OpenParen YearMonthUA CloseParen UASymbol;
  Level2YearMonthDayUA : OpenParen Year CloseParen UASymbol Dash Month Dash Day UASymbol;
  Level2YearMonthDayUAParenUA : OpenParen YearMonthDayUA CloseParen UASymbol;
  MonthKnownYearUA : Year UASymbol Dash Month;
  MonthKnownYearUAParenUA : OpenParen MonthKnownYearUA CloseParen UASymbol;
  
  // ***********************   Level 2: Parser Rules   ************************ //
  
  