anchor.diff:      | longYearScientific
       | seasonQualified
       ;
  -partialUncertainOrApproximate
  +partialUA
   	: MonthDayKnownYearUA | MonthDayKnownYearUAParenUA
   	| MonthKnownYearDayUA | MonthKnownYearDayUAParenUA
   	| YearDayKnownMonthUA | YearDayKnownMonthUAParenUA
  
positive.code:     | DigitOrU DigitOrU U DigitOrU
      | DigitOrU DigitOrU DigitOrU U
      ;
  YearMonthWithU : Year Dash MonthWithU | YearWithU Dash MonthWithU | YearWithU Dash Month;
  MonthWithU : ZeroU | OneU | U DigitOrU;
  DayWithU : U DigitOrU | OneThru3 U;
  YearMonthDayWithU
  
negative.code: /**
   * This is an Antlr4 grammar for the Extended Date Time Format (EDTF).
   * EDTF specification website: http://www.loc.gov/standards/datetime/
   * Version of the spec supported: Draft Submission, updated September 10, 2012
   *
   * Author: Kevin S. Clarke (ksclarke@gmail.com)
   * Created: 2013/02/06
   * Updated: 2013/02/23
   *
   * License: BSD 2-Clause http://github.com/ksclarke/freelib-edtf/LICENSE
   */
  