anchor.diff:      | '02' Dash OneThru29
       ;
   
  -YearMonth : Year Dash Month;
   YearMonthDay : Year Dash MonthDay;
   Day : OneThru31;
   
  
positive.code: // ***********************   Level 0: Parser Rules   ************************ //
  
  level0Expression : date | dateTime | level0Interval;
  date : Year | YearMonth | YearMonthDay;
  dateTime : YearMonthDay T Time (Z | (Plus | Dash) ZOffset)?;
  
  // *******************  Level 0: Interval Parser Rules  ********************* //
  
negative.code:     | Year uaSymbol Dash MonthDay uaSymbol?
      | Year uaSymbol? Dash partialMonth uaSymbol Dash Day
      //| Year uaSymbol? Dash partialMonth uaSymbol (Dash partialDay uaSymbol)? // works
      | Year Dash Month uaSymbol Dash partialDay uaSymbol
      | Year Dash Month uaSymbol Dash Day
      | Year Dash Month Dash partialDay uaSymbol // next one(?)
      | Year Dash partialMonthDay uaSymbol
      | season uaSymbol
      ;
  